I really enjoy giving gifts, so personally, I would jump on the opportunity. That's just me, though. Maybe a stocking with some candy and something small that all kids enjoy, like those puzzles where you have to get all the rings through a maze or something. Then you can just buy a generic amount, and not have to worry about if someone doesn't come.
OR, buy a puzzle (3D, maybe?) that they can all work on for some adult quiet time.
PS -- I think 30 is the age where people start expecting real adulthood.
PPS -- I think it might be embarrassing if some of these families bring YOU gifts, so again, I'd recommend have a backup plan. Play-Do is super easy.