A tool that is a very useful fix gera tool it the Pedros fix gear tool. Hub wrench, lockring spanner and a couple of other functions i have never used. But the wrench and spanner are both first class every day tools. The spanner is a also much better than the Park spanners for the bell shaped 12 tooth lockrings.
I ride the road fixed, flip-flop and both flip the wheel around and change cogs mid-ride often. I carry that Pedros, 6, 5, 4, and 3 mm Allen wrenches, a spoke wrench (sometimes), patchkit, 2 tubes, tire irons and sunscreen. All get used enough to be worth carrying. I am rarely caught short. 6 mm Allen - stem, 5 mm - brakes, stem, 4 mm - WB cages which go on and off frequently, 3 mm - dropout screws which I sometimes set for my smallest cog. Makes setting the chain correctly when I am brain dead from a hard climb easy.) There are other tools that the bike requires, but I have so seldom needed the crankset tools, pedal tools and bearing tools on the road that carrying them isn't worth it. All this fits easily in a small toolbag with room for one more something. (The Pedros tool slips into straps I sewed to the bottom of the bag, secured with a Velcro strap. Makse access fast.)
This has been enough for the two Cycle Oregons this bike has done. (Well, not quite, but the rest travels with the camp gear. I ride in luxury with different handlebar/stem/brake setups for flat and hills. It takes the 6 mm, 5 mm Allens and a 10 mm box wrench to change the setups.)
Ben