i normally just dump my camera[s] in my bag.

beware though: i broke a couple of plastic zoom lenses like this. since then i got a couple of prime lenses and haven't had a problem since. [just remember to keep a lense cap and a UV filter on the lense at all time. they're cheaper than new lenses]

otherwise, you could get some replacement foam for a flightcase [should be available from any decent photo/audio/electronics store for about £10] and cut it to fit one of the pockets of your bag.

[edit]
oh yeah: always remember to close your bag before swinging it over your shoulder.

d'oh!
[/edit]

fsnl
sparky