My main tool set is a Topeak Alien II, which has a very good selection of usable tools. I also carry old fashioned open ended wrenches and an adjustable wrench, as well as a few Torx and Allen wrenches for the odd sizes I occasionally come across. Plus chain links, tube stuff etc as mentioned above.

I carry more than I need, but I have been able to help a lot of folks deal with problems along the side of the road and trails.