Mr. McGroovy's Box Rivets
When I was a kid, I spent countless hours trying to build stuff out of cardboard, using tape, glue, thumbtacks and paperclips to hold it all together. More often than not, whatever I had constructed would fall apart pretty quickly. With a box of Mr. McGroovy's Box Rivets, my problems would have been solved. If you can ignore the dumb name, these are a pretty cool idea: interlocking plastic rivets that you can use to attach bits of cardboard to each other, making cardboard-based construction much simpler. Just one more tool in a kid's (or creative adult's) arsenal. $5.95 USD.