Bottle of Nintendo Game Cleaning Paste. Highly effective at cleaning dirt and grime from Nintendo game contacts. Specially formulated to clean metal contacts on NES SNES and N64 game cartridges without causing any harm. Enough to clean at least 25 games.
Also check out these other Nintendo Cartridge Cleaning accessories:
Nintendo Cartridge Cleaning Rinse
Nintendo Cartridge Opening Tool (3.8mm security bit)