Lightsabres
Connecting steel rulers across the terminals of the batteries of those lab packs. These rulers were then used as swords, which let off* an impressive flash of voltage whenever they connected.
If anyone's ever connected two 3ft steel poles to the mains and fought with them, I'd love to hear their stories. I never had the balls.
*Hurrr... let off...
written by Co*rade *let*h, approved by Log

We found two fluorescent strip bulbs discarded intact out the back of the sweet shop.
It turns out only one of them breaks under impact with each other, showering you both with shards of glass and toxic dust.
Like Conkers for REAL men.
written by Go*ty G*tty, approved by Mansh