plastic tarp from camping store, check!
park repair stand, double check.
bag of latex gloves from my girlfriend's lab, you betcha.
simple green, rags, bike lube, yessiree.
the key for me is up keep. dont clean your bike once a winter or you will drive yourself nuts. once a week seems to keep the cassette and deraileur in check but i wipe down the chain and relube it every few wet commutes. i dont worry to much about chain maintenance though. i just replace them every 3 months or so.