A Neo Geo 2-slot.
One fighter (Garou if you can afford it, any well liked KoF or Sam Sho otherwise).
One other (any Metal Slug, Bust a Move, Windjammers, Shock Troopers, Aero Fighter 2).
Cycle out carts once a month. Low cost to bring in, easy to rotate new titles in so things don't get stale.
Ms. PAC always does well on location too.