My wife lined up a trip with another couple to Cancun, at a nice all inclusive place. I've never been to Mexico, or to an all-inclusive. Even though tips are supposedly included, I've heard you'll get great service if you tip the staff a dollar or so, as they could use the funds, but another friend said not to tip. Thoughts on that? I've also heard to drink only bottled water. Any tips here from experienced Mexico travelers?