I find that I don't need to eat any extra food for regular commuting. Of course, I've got a spare 20 pounds of reserve body weight, but just eating what I would anyway (a bit less than I used to before I started biking even) my weight stays about the same. Of course, for long distance recreational rides, I'll bring along a food bar or two.

I use the gear tracker at mapmyride.com. I noticed recently that even my most expensive tires (Ultremo R.1's) have only cost me about 10 cents a mile so far and are still going strong. I compared that to the cost of gas, which I think I figured at about 12 cents a mile, and immediately resolved never to buy cheap tires again.