I like all of my accessories, but it's a real PITA to have to strip them off of the bike, especially when locking it up just so I can run into a store, bank, etc. I have front & rear lights, cyclocomputer, Airzound, seat bag full of tools & patch kit, pump, and a detachable mirror. Fortunately, everything but the pump can be stuffed into my helmet for a quick pit stop.

I don't ride with music, but I'd be interested in giving the BioLogic CycleTunes Speakers a try.