I keep metro and Kanamycin on hand. Both can be found at Angels Plus. Metro is cheaper from Jehmco.com but they don't sell Kanamycin anymore. However, they do sell Neomycin. Nitrofurizone is another good med to have on hand.
Meds aren't usually an immediate requirement and are only a day or 2 away if needed. Take care of your water and hopefully none will ever be needed.