I have a friend who does this very thing, and he has several different devices that he brings to his gigs, and uses one or two per song: all contraptions with foot pedals, some have mallets that strike a drum or a wooden block, and another operates a cymbal. He's quite interesting to watch, especially because he also plays lefthanded on a right-handed guitar (with the resultant creative chording). One thing that's always puzzled me, though: I can't figure out why he has a right-handed cutaway!!

Another acquaintance who used to come to my open-mike nights back when I hosted 'em would actually attach things to himself, like a tambourine strapped to his leg or a cymbal under his shoe. Much more awkward and much less professional-looking, IMO, but it worked for him!