There are preparations of powdered antibiotics available in bird or fish areas of pet stores; you can get them through agricultural supply house as well, but those are in HUGE quanitites. The ones for birds and fish are usually an ounce or so of powder which will last a long time if kept in the fridge.
I keep antibiotic ointment with pain reliever for the meeces and for my self. I have a large mousery, and I do occasionally get perforated by one of the little buggers. Oh, yeah, bandaids. The ointment is good on crusty scabby wounds to keep them from drying and cracking. Hydrogen peroxide is good to have around to. I keep saline solution around; it's good for so many things from washing out wounds to rinsing eyes. Often an irritated looking eye can be relieved with a good rinsing with salt water or prepared eyewash.
I also stock generic Benadryl syrup to use for itchy meeces or for meeces with chronic respiratory problems. It's easy to use; I just paint it on their muzzle and they clean it off, thus ingesting it.
