[bombcar]

If you get the right kind of paint/marker you can mark the bolts with the same color as the wrench, then you can see what wrench you need from many feet away.

Or just grab the 10mm, it's always 10mm.

[ndsipa_pomu]

I can't think of any 10mm bolts on my bike. Most of the time, it's 4, 5 or 6mm hex bolts.

[eschneider]

Nail polish works great.