How many cookie bags needed for guests?

I would recommend getting enough for each guest. And don't forget about your vendors.

I would base it on households instead of individual guests, so at least on bag per household.

For something like cookies, I would over order, say 225-250. If there are kids involved they may take more than one. I know our candy buffet was a huge hit with both kids and adults. We had maybe 20% left in the end, but we also put out the good stuff like Reeses, and Hershey kisses, and Kit Kats.

If you invited 211, get 225-250 bags if they are filling then themselves. If you are pre-filling them get 211.