This is very nice of you, OP. It would be nice to leave in the room: bath towels, phone charger, wifi password, a toothbrush and tooth paste, a few water bottles, and a little container with band aids, neosporin, qtips. I think a robe is unecessary.
For food, I would not leave anything in the room but would point out where we keep pantry items and say to help themselves to anything in there or fridge. I’m not clear if you are looking for food ideas? If so, I’d say standard stuff like bananas, apples, oranges, yogurts, cereal and milk, cheese, bread (toast), granola bars, chips, yogurts, etc. And yes for dinners make enough for 4 extra teens even if there are only two staying with you

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