For me, it'd be a packet of Trident Layers from Walmart.
Just remembered that when I was in Kindergarten, I constantly snuck legos into my pockets almost every day that we had break time. I was only caught near the end of the school year when I tried sneaking a ship baseplate into my pocket. It didn't fit. Turns out that I've been a little scumbag since then.
What about you guys?