Thanks so much for the info everyone! I'm surprised there is that much of a difference.
Sounds like we're on the right track then. We arrive a day before the guests (us, Wednesday, guests Thursday). We'll have a car and our first stop will be to the grocery store to pick up some sun products, bottled water, soda and some dry snacks like chips for the bags. I also like the idea of the Belgian chocolates if I can afford them. Dutch cookies may be a good touch too since my family is Dutch. (Or at least we had grandparents that came to the US from the Netherlands.) Then maybe stopping back the day they arrive for some fruit and maybe a few other cold snacks since all the rooms at the Marriott have refrigerators.
How about a place that has a good selection of postcards and stamps for purchase? I was thinking of putting a few stamped postcards in each bag. One idea I came across was taking one postcard for each bag and pre-addressing it back to us, asking the guests to send it at the end of the weekend with their favorite memory from the trip so we'd have them to add to a scrapbook later.
I wish we'd have time to go to a flea market. Instead I'm planning to bring bags with me. I was hoping to find something that could be used as a beach bag. The best I've been able to find so far is these:
http://www.blissweddingsmarket.com/store/000414.htm. I'd like to do one bag per room which could be about 15 of them.