Making Bogies.
For those on the other side of the atlantic, you would take the axles and wheels from an old silver cross pram and connect them together with a piece of wood allowing the front axle to swivel via a bit of string. if you were posh you'd cover the wood with a bit of old carpet. You'd then find the biggest hill you could and have races down it.
Jumping over your mates with your bike. You'd build a ramp and get your mates to lie down and you'd jump over them evel kinevel stylee.
I once did seven. :)