From our Australian correspondent, Ian Gunn:

BOILING BOTTLES: When rinsing plastic soft drink or juice bottles, half-fill with hot water, quickly pour it out and invert the bottle on a smooth surface. Sounds like bacon frying, and worries cats.

TENNIS BALL CANNON: You will need a can opener, a tennis ball, four beer cans, gaffer tape, methylated spirits and long barbecue matches. I don't know if Euro-standard beer cans are big enough but they need to be of larger diameter than the ball, obviously. Remove the tops and bottoms of three beer cans, then tape them into a tube. Tape this onto the end of the remaining can so that its ring-pull hole is inside the tube. Punch a small hole near the top of the side of this can. Insert a small quantity of methylated spirits (you may need a funnel). Put the ball in the tube and, with your thumb over the side hole, shake the whole thing vigorously to cause the spirits to vaporise.

Place on ground and carefully insert burning match into side hole. DO NOT USE INDOORS. It might be an idea to use a match as a wick in the hole and to retreat to a safe distance.

And from our Californian correspondent Allen Baum:

How could you leave out the pop-tart blow-torch? Or the pickle lantern? The liquid oxygen barbeque starter? (all thoroughly documented on the web). You also might try grapes in the microwave for a real light show.

One of the favorite pastimes of my, um, past is a hot air balloon made with a candle and dry-cleaner bags (I don't recall if they exist in the UK -- they are extremely thin, clear plastic bags about 2 feet across and 4 feet long). In any case, they make extremely good excuses to call in UFO sightings on a clear summer evening.

And finally, a real simple one. Take a 2 liter plastic drink bottle. Fill with crushed (crushed because...how else will you get it in there?) dry ice (which I'm assuming you can get somewhere), less than 1/3 full. Screw on the cap tight -- quickly, and stand waaaay back and cover your ears.

None of these compare to emptying a large propane cylinder into a dry well and (figuratively speaking) throwing in a match, of course. [But the Plokta editorial team cannot recommend this, you understand.]