longboarding at night, sneaking out (only applies if you're under 18), just driving around looking for skate spots and seshing them, late night mcdonalds runs, go to a community pool like 1 hour to 30 minutes before close and normally you can swim for free (diving board sesh?), launch model rockets, do dumb stuff with model rocket engines, build random things that explode and/or shoot projectiles
a further note on the model rocket engine thing, last summer my friends and i attempted to build a miniature car out of a tech deck and some card board and then propel it with a model rocket engine. we tried to build a spoiler to keep it from getting airborne, but it didn't work. it got airborne and hit my friend in the face and he had to get 7 stitches in his forehead. in retrospect, we probably should have weighed it down with something.