My mate just got back. He said he spent most of his money on tips. Which was usually about $2 a tip. He'd only spent $50 in the first week and $30 of that was a taxi!
He only spent £500 in the whole two weeks he was their and some of that included a trip round the local town (Cancun) and a swimming with dolphin trip. My mates not shy when it comes to spending either. I think he went on a sea fishing trip and a scuba diving trip which was free provided by his hotel, (also 5* fully inclusive "Moon palace" i think it was called.). The swimming with dolphins cost him $137 whatever that is and took a whole afternoon. I don't think you'll need much to be honest, i remember him saying that the clubs in cancun cost the most at around $25 entrance fee which included free drinks all night.
It certainly looked nice in the pics he showed me yesterday , he drove a golf buggy to get round the hotel campus. He said he didnt lift a finger all the time he was their, the hotel staff did everything for him, replacing his drinks just before he'd finished his last glass/bottle.
You'll have a ball mate, i'm jelous!