UV and cleaner shrimp in the tank. Hydroplex in case I have to pull a fish to medicate. I put the fish into a QT and pull him out occaisonally for a dip. I don't use any medications in the QT, just really strong water quaility.
Neosporin, hydrocortisone cream, Benadryl and Pepto-bismol.
...but those are for the reefkeepers (in association with the reef-keeping.)
Any fish antibiotics we had expired a long time ago. I think we probably have some old maracyn, and maybe copper. Malachite green, too, if I remember right. Needless to say, I don't keep any lying around. I'm more into prevention than treatment, and have cleaner shrimp in the tanks.