It should be noted that there are a few souvenir stands near the cafeteria and museums.
All manner of Mayan handicrafts are sold here, from small carved animals to stone Mayan statues. You can also pick up a t-shirt if you need a change of clothes. Although prices are rumored to be lower in the nearby city of Flores, you can bargain with the vendors here and we found the prices quite reasonable. This is a great place to pick up gifts for home, and I brought home some obsidian jewelry for my mom and a Mayan goddess statue for myself.
If you need snacks or water, here is the place to go. After our unpleasant dining experience at the Dining Lodge, we ate entirely from the vendors here, getting oreos and pretzels. These were not the most nutritious meals, but we knew they were safe and wouldn't cause further illness.