Nintendo Cartridge Soap
However realistic these may seem, I'd advise against sticking these in your classic consoles. It's a shame, though -- I've been looking for a copy of Chrono Trigger.
Nintendo Cartridge Soaps come in a variety of appropriate scents, including "Mountain Dew." Prices range from $3.75 to $12.59, depending on cartridge type and size. If you'd like to purchase soap for the geek in your life, definitely check out DigitalSoaps on Etsy.