That's kind of short notice for food prep, especially without getting a firm guest list.
It might be nice to just have everyone pack a lunch, that way you dont need a head count ahead of time, and anyone who happens to be free that day can be encouraged to come, and its no big deal if someone cant make it (which is usually a guy bringing a key part of the meal, like plates, cups, or forks
).
If it gets a good turnout this fall, maybe we could set up a pot luck for next year, whether a year form now in the fall, or next spring.
Food just adds a LOT more setup, prep, organization, etc. that would become challenging on such short notice.
...that said, I'm sure noone would object if someone brought a snack or something to share.