What do I need to turn my bike into a reliable form of practical transportation?

Maybe this is kind of irresponsible, but I bike commute without carrying any tools or supplies. I figure hauling a bunch of crap around will make me less prone to actually get on my bike and go. I'm willing to deal with the occasional crisis as it comes up, and I'm slow enough with repairs that if I get a flat on my commute, I'm going to be late to work whether I can patch it up then and there or not.

There are lots of great multitools out there, probably just as good as http://www.amazon.com/exec/obidos/ASIN/B000FIE4AE/metafilter-20/ref=nosim/, but I wanted to mention that I have been car-free and commuting everywhere by bike for 3 years and nothing has ever happened that I could not repair on the side of the road with that tool, a pump, and a patch kit or spare tube. Get those and ride, you'll be fine, and your future needs will reveal themselves as minor inconveniences along the way.

I read your post, and want to stress that again. I feel like I ought to be able to figure this out on my own but for some reason keep coming up against some kind of internal inertia that's prevented me from getting this together, so I'm asking you guys for advice in the hope that it will motivate me to make this happen and join the ranks of happy bicycle commuters everywhere. Just go ride and have fun. It's not about tools, they're not what's keeping you off the bike. Tons of people have great bike equipment collecting dust in their garage, you don't want to be them. Be safe. have fun.

Not always practicable or possible, but leaving some work clothes at work (pants are a good candidate--I wear black jeans at work, and as a fat bastard they take up a lot of room in a backpack).

The first thing that I found out (and LOVED) about bike commuting was that it doesn't cost a lot of time to ride on the smaller side streets where possible. Highly recommended--I have a very specific ride I do nowadays (not really a commute) but I go a slightly different way every time. Makes it much more fun. About 13 miles round trip.

Nthing the helmeting... it will make you more confident to ride out into traffic. I'm also a huge fan of making eye contact with drivers, especially drivers coming up from behind me on my left. I feel much more secure once we've both acknowledged our mutual existence.

You don't need a spare link to use a chain tool. You can just take out the broken link and close the chain back up. It's not ideal in the long run, but it'll get you home. I carry a chain breaker/multi-tool combo, tube, pump, and tire levers. Keep it cheap and light or you won't want to carry them. I always bring a water bottle and sweater in case something unplanned happens, but I'm commuting 20km in the country with nobody to save me from disaster, it's a bit easier in urban settings. Lastly, yeah, stay on top of maintenance and visibility. Learn to do your own basic maintenance, you don't want to be going to the shop every time your chain needs oiling. Look though: If you don't have everything ready the first time, don't sweat it. Just go ride. It's supposed to be fun and relaxing; you're not going to want to ride if you're stressing out and hauling a garage worth of tools around with you. As you ride more you'll get more serious about it, there's no need to rush and stress.

gloves. minor mishaps can often shread your hands, and proper ulnar nerve padding can prevent hand fatigue. plus, it is sometimes nice to keep your hands clean when you have to lean on something or press a grotty crossing button. there are gloves for every season and you should definitely try before you buy.

Oh! And a rearview mirror that clips onto my left handlebar has saved my bacon more than once, and IMO is vital if you have to make any left turns in traffic along your route.