A bag of holding opens into a nondimensional space: Its inside is larger than its outside dimensions. Regardless of what is put into the bag. Generally found in tabletop and RPG games, such as D&D or Pathfinder.
Buttons are a great way to show off your geek cred. And honestly you can find that just about anywhere for pretty cheap. I've got stuff from Dr. Who, Alice in Wonderland and Star Trek on this one.