Where I was cruising in Mexico -- which admittedly was some years ago, and was on the Pacific side -- the best provisioning
was to be had in two different places -- the markets, and at Costco.
At least in the part of Mexico where we were, I thought the provisioning
was excellent, very good and very cheap
, and I wouldn't have felt necessary to stock up in the U.S. other than things you really want to have, which are harder to get there. I'm not sure what that would be -- the variety of food
available is excellent, and we didn't lack for anything we wanted -- but you might have some special tastes.
Also eating out in Mexico is a real joy, so you might not be cooking
as many meals
on board as you are used to.