8,10,12mm work for 90 percent of the things you may need to do on the trail. Plug socket is a good idea, along with a multi-tip screwdriver and pliers. I carry a few different length 8mm flange bolts, a spare footpeg bolt, and a small can of fix-a-flat
I used to cut a roll in half, then cut each of those halves in half. The quarter roll is plenty (as if you could ever have enough), and it is already in pieces a few inches long so you don't have to tear it.