Five Crazy Science Stunts You Won't See at School

The sodium+water reaction is pretty common in high school chemistry classes, and I've been around some larger examples when they actually have a pond near by. The LN2 rocket and various dry ice bombs I've seen at quite a few demonstrations too, when probably those are ones likely to be frowned upon by administration.

The pumpkin one can be done with alcohol instead. I wouldn't do the acetylene version myself, as there have been a few too many incidences with acetylene in a confined space suddenly exploding a lot more than expected. Some people I knew had setups (not pumpkins though) that worked fine several times, then got knocked on their butt and were lucky no shrapnel was involved.

The microwave oven transformer mod is a fun one that comes up some outreach demonstrations, and is essentially just doing what a primitive arc welding unit will do. In fact, you can build a primitive arc welder with a few more cheep parts.