Thanks for your feedback everyone, not having been to Mexico yet I had no clue as to what the facts were, obviously!
Ian and I didn't take anything off the ship in the Bahamas as we left were back on Sensation for lunch.
We'll keep that all in mind but will most likely eat lunch on the ship before we debark for the beach in Cozumel, since the timing will be right for that. But it's good to know that if we do want to spend a few dollars on a snack while there, that it is safe to do so.
Of course, I really avoid buffets anyway - at home or away - with people breathing, coughing and sneezing on or near them.