In Toad Scramble, when players have Waluigi in the party, he can roll a 6 to add to the player's total roll, or roll a -2 coins slot, causing the player to lose 2 coins instead. (mariowiki.com)
You can get the «retro» style from Think Geek's site (has woodgrain front and oldschool 25c coin slot for the power indicator), or a less 80's arcade style from ion audio directly. (toucharcade.com)
Officially licensed from Taito, Space Invaders «creator, the backpack is modeled after the original arcade cabinet and even has a functional coin slot. (dailydot.com)