Depends on the 5yo boy. My DS5 is not into super heros, but some of his friends are. He outgrew cars & trucks a couple of years ago, as did most his friends, but some are still into it. For my DS5, it would be dinosaurs or Star Wars all the way.
The theme of the party should really give you a good idea. If the theme is spider man then super heros might be the way to go, for example. When I don't know the child well, and didn't have the chance to ask the parent what the interests are, I go for some general things. Some of those gifts that I have given this year include Lincoln Logs, Pogo ball, bubble gun & sidewalk paint, outdoor tetherball (portable) set, gift certificate to Build a Bear (very close to Christmas birthday), slip-n-slide, a couple of games and very newly released DVD. And always include a gift receipt just in case.