All that "leaping tall buildings in a single bound" stuff is bound to make a superhero hungry. If you're having a lunchtime party, a sure bet is a superhero sandwich bar. The kids might not get the pun, but they'll love making their own sandwiches. Just get a variety of lunch meat, cheese, breads and condiments, and you're good to go. Tiny superhero-flag garnishes, however, would really put things over the top.
A cupcake bar would be another definite hit, but be sure to kick things up a notch and make things truly "super." Mix up some intense neon-colored icing in a bunch of different colors, and set out tiny action figures for cake toppers (plastic superhero rings would work well as toppers, too). Things could definitely get messy, but that's part of the fun, right?