What are some practical gift ideas for 4 year old boys?

I know they are into TMNT and "play fight" a lot-- not so into letters, construction, cars, etc.

I'd rather not do regular toys-- their home is pretty loaded with toys and they have a new baby so I'm thinking I don't want to add to their Lego collection this time, either..

Any great book titles or board/cooperative games for this age? I love the game/small gift + coordinating book idea but can't think of specific things.

I also thought of nice personalized beach towels.... yay/nay?