I like the Topeak mini one w/ a chain tool. It's lightweight (well, fairly) & has everything except a knife on it. I would say DO get one w/ a chaintool & carry a missing link/quick link appropriate for your chain. It's really a fairly easy fix (am sure your lbs would show you how). Briliant if you break your chain, also brilliant if you break your rear derailleur - you can turn your bike into a single speed. I came across a guy who had a rivet crawling out of his chain - w/ a chain tool & a missing link it was literally less than a 5 min job (& boy was he impressed). The other think I always pack (mainly in case I have to do any stuff w/ a chain) is a pair of disposable gloves.