In reply to J1234:
It all rather depends whether you want to deter a committed bike thief or an opportunist passer-by. I just use one of those reinforced HipLock zip ties as a cafe lock to deter the latter. If there are two of us, then we face the bikes in opposite directions and zip tie the pedals together (as above). If you're on your own, try to tie it to something solid so that someone can't just tuck it under their arm and walk off. Pedals are good as they have so much movement it's hard to twist a lock to break it against the thing it's fixed to.
The other thing you can do is undo the front QR so that the whole thing turns into a spectacle if anyone fancies their chances (this is particularly effective on one of my bikes that doesn't have retaining tangs on the front fork) - just remember to do it up again.