I would ask each attendee to bring something for the event, whether that's some juice or soda, chips, cookies, brownies, baguette bread, ...paper plates, napkins, cups... think along those lines. That's what we've done for each event and it's always seemed to work out well.
If you post what you're thinking of bringing, it might help in preventing the sort of situation where we end up with 30 of the same thing. Hasn't been a problem in the past, but couldn't hurt.
If you have any sort of freebies/handouts of interest, bring those along, too. Think in terms of the sort of stuff you might get at an industry trade show: little keychain or pen lights; pouches; batteries; pens/pencils; Fluke 189 DMM for the host.
(...okay, the Fluke was wishful thinking on my part.)