And the official rules, according to the flight attendant, are that every person is allowed 1 liter and any bottles over that amount are subject to a whopping $2 tax. Yes, that's TWO dollars (I want my 2 dollars...anyone remember "Better off Dead"?
Now this is flying into Dallas--like Gordon said, each state might have different rules.
However, on the itemized part of the customs form, all you do is write "Alcohol" and then whatever $$ amount you spent. I usually put $20, that way they don't get curious about how many bottles I have. I usually bring back 3-5 bottles (not a lush but my friends are
You don't have to list each item individually--just group your purchases into categories.
I do have to comment on the use of credit cards though...there IS a 16% service fee for using a credit card on Cozumel. This is due to the Cozumel banks, not your credit card company. The shop owners aren't going to eat that cost, so if you want to use a credit card, YOU must pay the extra fee for the convenience.
I don't recommend using credit cards down there--take cash, traveller's checks or take your debit card and get pesos from an ATM. Do NOT use your debit card for purchases--some unscrupulous individuals could wipe out your entire bank account. Most stores will give discounts for cash and it's just less hassle all around.