For a start, you want alley keys and TorX T20 t-handle, not bits that can be lost in the grass, the dust or the mud. Bernd Rohloff publishes a list of tools near the front of the handbook.
Basically, it comes down to
Allen keys 2, 2.5, 3, 4, 5, 6, and whatever your cranks and pedals take, 8 or 8 and 10
Torx T20 T or L handle tool
Rohloff sprocket tool
Crank extractor
Bottom Bracket tool
8x10mm open flat wrench (Draper makes one, or buy a universal brake adjustor at the motor factors and grind it flat. The Park Tools version is limp stamped steel, yech. This is good for changing gears on the Rohloff EXT box if the cable breaks, and tightening lamp and mudguard bolts)
(If you need more flat wrenches, replace the 8x10 with a small adjustable wrench)
Chainbreaker (unless you use magic links)
EBB tool
50ml bottle of Oil of Rohloff (chain oil, can be used elsewhere in an emergency, this stuff sticks like the proverbial to the baby's blanket)
Spoke key
A tube repair kit and tools
A tyre sock
If you actually want a multifunction tool, a good one is the SKS Travel Tool, see
http://www.sks-germany.com/?l=en&a=product&r=tools&i=7000&TOOLBOX%20TRAVEL which includes the valuable Torx T20 and 2mm Allen as extra keys you can swap in. I also have the CT-Worx, which has an even wider range of tools, but lacks the T20 and 2mm Allen, which will then have to be carried as extra whole tools. These are superior tools at very reasonable prices (for German-made tools!), carried by SJS:
http://www.sjscycles.co.uk/sks-toolbox-travel-18-function-multi-tool-prod19468/ http://www.sjscycles.co.uk/sks-ct-worx-20-function-multi-tool-prod19467/ Andre Jute