A few tips on tulum:
• the only footwear you need are flip flops. sand is everywhere and heels are dumb, so are regular sandals. sneakers aren't a bad idea if you're planning to exercise.
• while most places use filtered water, i would say bottled is still best. even for brushing your teeth.
• bring small unmarked bills with you. seriously: cash is king, and every cab ride seems to cost about $7. You'll be hard-pressed to find someone to give you change, so the more singles you have, the cheaper things will be.
• the other thing is, you have a long ride from the cancun airport to tulum. but it's shorter if you have your driver stop at the 7-11 right outside of the airport for beers and chiccarones. yes, really.