Fabulous trip! Just a few logistics that could be tightened up:
1. Explain that AGI will have our round-trip ferry tickets and will collect them back when they drop us at the hotel. Our tickets were not given to us until we asked as we were rushing to the ferry, and then no one asked to keep them, so I tossed them.
2. Better communication between ferry dropoff and pick-up in Isla Mujeres. There was no driver waiting for us when we got off the ferry because it was assumed we'd be on the 9:00 ferry instead of the 8:00.
3. Tell people to bring ~$100 per person for tips to the boatmen.
4. Packing list could be pared down. No need for 3 pairs of shorts or 5-6 T-shirts. Because MarAlliance gave us dry bags and a long-sleeved shirt, we didn't need to bring those either. We also didn't really need a nice outfit for dinners because IM is so casual.