My Bianchi Eros carries the least: just a spare tube and patch kit. (A full-size frame pump rides along the seat tube.) My fixed-gear adds a PDW 3wrencho for the rear axle nuts, and it can be a tire lever if anyone around me needs it.
My rando bike carries the most tools, since it has the most fasteners and takes me on the longest rides: spare tube (or two), patch kit, allen wrenches in 2/4/5/6mm, spoke wrench, couple feet of duct tape in a small roll, some zip ties, and a pair of fingernail clippers. The bike has a couple of 8mm, 9mm, and 10mm fasteners here and there, but I just double-check that those ones are secure before long rides, rather than taking that many more wrenches with me.
