So, I wrote earlier about what you should know if you wanted to get started riding to work. Now I'm going to write about a bunch of stuff that isn't necessary on the first day you start riding, but I think make the whole experience easier.
Your car is prepared for most basic trouble. It comes that way from the factory, and most folks add a few bits. So, for example, my wife's car has a spare tire and jack, for flats. It's got a jumper cable, some warm clothes, a flare, and some basic tools.
By comparison, your bike comes with nothing.
At the very least, you want some way to handle tire problems. The exact tools required are somewhat up to what kind of bike you want and how long you want to spend on the roadside. At the very least, you want a patch kit, a pump, and tire irons. Patching inner tubes takes a bunch of time, so most folks just carry a whole spare inner tube (it's cheap and lightweight). Most folks carry a multi-tool for adjustments. Duct tape is handy for emergency tire repairs and other troubles. I often times carry water and food, even if I probably won't need them. And I also carry some spare parts.
My first girlfriend, before I knew her, broke her collarbone going over the handlebars while biking. She blamed grabbing the front brake for why she flipped the bike.
I had always instinctively grabbed both brakes before. But eventually I did some research and found Sheldon Brown's site and started to adjust my biking style. According to Sheldon and I've found this to be true, on dry pavement, the front brake and just the front brake is sufficient to stop you. If it isn't, you need brake work.
But what about downhills? Don't you flip the bike over this way? Not if you are ready for it! I discovered this while doing some controlled tests. If I hit the front brake on a downhill, I need to be braced against the handlebars. If you are used to what this feels like, it'll be instinctive. If you aren't, you will go flying.
Thus, if you are riding, unless you know you shouldn't be using it, you should prefer the front brake because then when you really really need to brake, you'll already be braced.
If you are descending on a street, you have a lot of energy to dissipate, far more than what would happen if you stopped at a sign or a light. Brake pads on the rims creates heat. If you are on a long downhill, that's a lot of heat and this can cause your tires to blow up. So you want to switch between front and back brakes if you are going to use your brakes going downhill on a street to control this.
If you are going on loose or slippery terrain, you can skid your tires. If you skid your rear tire, it's recoverable but dangerous. If you skid your front tire, it can quickly get unrecoverable. Either way, you'll end up fishtailing from side to side and get dumped off the bike. If you are steering into a turn, it'll get worse. Thus, on uncertain terrain you really want to use both brakes and modulate both of them so that you don't skid either wheel.
But, either way, if you never use the front brake, when you really do need it (and you will, one day) it'll scare the hell out of you and make a bad situation worse. If you always use the front brake, you will be used to it.
I've found that most folks tend to want to keep the seat adjusted so that they can have both legs on the ground while sitting on the saddle. Except modern bikes have the pedals much higher than older bikes, so if the seat is adjusted that way, you will probably have painful knees and won't be able to bike as fast.
There are a lot of little adjustments that can be made back and forth to properly fit a bike to you. You can do them yourself by figuring out what hurts or feels uncomfortable or you can have a professional do it. Picking the right size of frame is very important as well. You really can't add extensions various places to get the bike adjusted properly if the frame is the wrong size.
Most bike stores try to do at least some level of this. Although I have had a bike store try to steer me towards a frame that was several sizes too small (probably because that's what the frame size they had too much of) and sometimes they won't get everything right, adjust it using older ideas that have been shown not to work, or not take into account the desired use, so you want to be careful.
Especially if you go from no physical activity to biking every day, the shock of change is going to hurt you when you start out.
For example, it turns out that the best saddle is an unpadded saddle that just supports your sit bones. This will give you a sore rear starting out... but if you have a nice big padded saddle, it'll be comfortable until you get a charleyhorse from not enough circulation.
It might seem more comfortable for your back to be fully upright, but it turns out that it's better long-term to keep your back angled somewhat forward (although not in the flat-back road biking position).
Your legs may be hurting a LOT and be somewhat stiff.
On the other hand, your knees, ankles, etc. are all not supposed to be hurting. Generally if something hurts, it means that your bike isn't quite adjusted right or you are doing something wrong. Most people can go from nothing to biking 5 miles per trip without any problems.
Nor are your genitals supposed to be numb. Or fingertips.
Cadence is the rate you turn the pedals. Tour de France people tend to shift a LOT to make sure that whatever the exact right cadence that gives them the absolute best speed and endurance is, they are pedaling it. Tour de France wanabees will spend a lot of time shifting like that, but instead just waste a lot of effort.
You can either make your leg muscles burn or get out of breath. If you pedal at a very low cadence, you are putting a lot of strain on your leg muscles, so they are going to start burning and feel altogether uncomfortable. If you switch gears and pedal at a very high cadence, your legs are going to feel just fine but you will start to get out of breath faster. If you spend all of your time pedaling at such a low cadence, eventually you are going to wreck your knees.
The number people throw around is an ideal cadence of 90 rpm, which feels awfully fast.
I find a lot of people will shift in the wrong direction going uphill, under the assumption that if they pedal at a low cadence and really push it, they'll have an easier time going uphill. I would try to upshift in the right direction but too far, which meant that I was pedaling at a massively high cadence and would get out of breath.
Finally, if you need just that little bit of power to get moving, you can get your rear off the seat and stand on the pedals. It's not sustainable, however, so if you are finding yourself doing it for long periods of time, you are doing something wrong. Furthermore, unless you know that your bike is in good working order, that's a good way to end up with your crotch banging against some uncomfortably hard piece of your bike with your bottom bracket (that's the thing the pedals are attached to) broken in two.
My college bike had nothing in terms of cargo accommodations. Not even a bottle cage. So I'd ride to class with a travel mug full of hot tea in my hand and a backpack on my back.
When I got my 7100, I wanted a bottle cage and maybe eventually a rack. I did get a little pouch that goes behind the handlebars before it got stolen but never got around to getting a rack.
When I got my Fuji, it came with a rack and two bottle cages. I quickly got rack webbing to carry stuff. That instantly made my life easier. I could carry lunch on the rack or a trunk bag with spares and tools. Eventually, I got pannier bags, which easily multiply my ability to haul stuff and are even handier than I'd expected them to be.
If I carried a week's worth of groceries in a backpack, it would have to be the sort of backpack that people use for week long hikes and I'd feel every pound on my back. But if I carry most of my groceries in my pannier bags and a few light things in the backpack, I barely notice that I'm loaded down. The nice part is that I leave them mostly empty with my normal commute load, so if I want to go to the grocery store, I can get a bunch of groceries real quick.
Unless you are just going to race, you need to have a rack. It's so incredibly useful and so much more comfortable that you'll wonder what you did without it. It's a pound and a half of extra weight for a sturdy rack.
This lets you do things that you'd think that you need a car for. Racks are often rated to let you carry 60+ pounds in back and 40+ in front, such that the limiting factor is how strong your bike frame and wheels are.
You don't want a handlebar basket. The problem is that, unless it's designed to work in conjunction with a rack, it's not going to be sturdy. If you look at how they do things in Europe, if they want to carry serious cargo, there's a rack, even if the rider put a basket atop the rack. If you look at the specifications of most racks, they list capacity by volume, not weight. If a weight limit is given, it's pretty much guaranteed that it's well below what any rack is rated for.
Check out my section on racks and my section on options for stowage that strap to your bike or your rack.
There's a lot of gear options here. If it's cold, add layers. If it's rainy, add rain coverings. All of these can be packed fairly tightly.
check my clothing section for more details.