Ummm....
Box of latex gloves.Otherwise everybody who drives the van has grubby hands....
Junior hacksaw (that way you know that amongst all the bolts you are carrying there will always be one of the length you need....)
Small vice, perhaps with a G-clamp (or two) to secure it to the step of the van. (I can lend these items if needs be)*Cough! - that's not an offer I usually make*
M5 tap. Srsly, a tiny tool to carry, and can mean the difference between 'go' and 'game over'.
The plastic Shimano tool for pre-tensioning the load on BB bearings where Hollowtech cranks are concerned.
No, stay with me.... for the moment, I speak with experience.
It was on a FNRttC to Whitstable, somewhere near the Dartford Crossing that someone (may've been CliveB, don't quote me) shipped a chain inboard, jammin' it like Bob Marley between the granny ring and the frame. Goin' nowhere.
I watched with much respect as Tim Hall flexed his chainset extractor (old, for some of us, stylee chainset - tapered cranks) and removed the chainset to liberate the chain.
Not something I would've necessarily considered doing at the roadside (on reflection - why not?) - but arguably the most expedient way of dealing with the problem.
Given the popularity of Hollowtech cranks, I have been carrying said Shimano tool on FNRttCs ever since.
It's a thruppence ha'penny tool, which weighs nothing and does a critical job, and I'm unaware of any other tool with which you could bodge the job.
This is teh thing of which I speak:
http://www.chainreactioncycles.com/...le&utm_medium=Shopping&utm_name=UnitedKingdom
I may think of some more things later.... like baby oil...