I used to make a very simple explosive with 2 then common household ingredients, the one that's safeish when still wet but goes off with a crack when it's dry. Pongs a bit too.
My mates and I would put it strategically placed on the scalextric track then have race. Go too fast in the chicane and bang, the car flys off. I didn't like it when my e-type Jag flew all the way down the attic stairs.
I also got into 6 of the best for proping up a sadistic teachers chair on matchsticks and putting some under the feet before lunch.
When he came back, he sat down, the chair went up, he ran out, I couldn't sit down for ages.
Just think of the trouble I would be in now but I can't say I regret it, he was a mean B*****
Chas