Any ideas for a warm, non-violent boy's costume for Halloween?

[babybouncer]

It's a big deal round here - we live on a new estate with loads of kids and knock on doors with pumpkins outside. I've promised DS (5) that he can go trick or treating this year, and he is excited about dressing up, but now I'm panicking about an outfit. I was just going to get something from a supermarket, but they look too thin for an October night and really scary (he's a sensitive soul!). DH is adamant that he must be something spooky and not just fancy dress - if he was a girl I'd have done a cat or a witch, but I'm not sure he will go for them, what are the more unisex/boyish alternatives?

Any ideas? Or links to shops?

Thanks for all the ideas, I quite wanted to do a wizard or cat, but DS has gone for a pumpkin outfit - bought a medium orange tshirt and hot-glued black felt mouth, nose and eyes on the front. Seems to be a winner.