The Cozumel Insider mentions bringing gifts to give out as well as cash for tips. Here is what it says:
What do you think??Cozumel Insider:Gifts/Tips - While cash is always appreciated as a tip for excellent service, sometimes a small trinket from your home country is more appropriate for a new found island friend. Many people from Cozumel seldom leave the island much less the country of Mexico. The population as a whole is exposed to a lot of merchandise in the stores, on TV and the Internet but availability is another thing all together!! Here are some inexpensive suggestions of things to stick in your bag just in case.
Music cassettes and or CDs (they dont have to be new)
DVD's (they don't have to be new)
Small keychain type flashlights
Small pocket knives (remember to put in a checked-in bag!)
Brass or stainless clips (fishermen cant get enough of these)
Small Address Books
Small scented candles
Perfume samples
Crayons or colored pencils/pens
Wine openers