All sorts of things, but I only stop to pick up tools and paper money. Recently, a flat screwdriver and a drywall wide putty knife. Farther back - 1/4" drive full socket set, 16" Craftsman adjustable wrench (score!), and a nice folding carpet knife. Loose allen wrenches. Loose sockets - of all kinds. Sometimes a useful box or combination wrench, especially 15mm ratcheting ones.

I'm holding in my hand a Park Tool AWS-9 multi-tool that I found on the road once. It's now in my commuting handlebar bag!