One day, when I was in the second or third grade, I had an epiphany about what was possible if you took a length of masking tape and folded it over. Do that and you can change it from an adhesive to a material. Before that moment, when tape would fold over onto itself, I considered it unusable, and I would throw it out, start over. What I figured out simple: folding masking tape over itself and layering it turns it into a pale, synthetic leather that is semi-rigid and could be fabricated into a wide variety of objects.
I consider this a major revelation for someone that age, also because this happened in 1976 or 1977, right about the time that duct tape was no longer an obscure WW II-era moisture-resistant adhesive. It was now in the toolbox, next to WD-40 and bailing wire.
Because I was seven or eight, I wasn't part of a DIY or handyman movement, which made me feel like a pioneer. With this masking tape leather I made small boxes, costumes for action figures, helmets for stuffed animals, mazes, the pouch of a slingshot. Later on my friends and I made whole suits of armor using cardboard boxes and the beige leather. We, of course, moved onto duct (duck?) tape and eventually made wallets. In high school I had a tape notebook. After college, I went through a spell of fabricating things with cardboard and hot glue. But it all started for me with masking tape.
My son is really amazing with LEGO bricks. They are his medium. I played with them too, of course, when I was young. I've noticed that many makers, hackers, engineers, and do-it-yourselfers identify LEGO bricks as a basic starting point for their activities. This doesn't seem revelatory to me because LEGO bricks are designed for this purpose. In fact LEGOs have turned away from their "open" roots to a more proscriptive thing these days: build the Millennium Falcon or Helm's Deep; here are the instructions and the special bricks. Michael Chabon has a great essay on this issue in Manhood for Amateurs. I recommend it.
In the end, the power of masking tape for me is the fact that is was not designed as a toy. It was created to assist amateur painters (real painter cut in). Turning this stuff into a helmet and breast plate for Winnie the Pooh was a hack—my first hack— and it established one important foundation for me: you don't have to use things the way their designers intended. This understanding is a requirement, in my mind, for creative thinking.