You will not find good weed in Mexico. Period.
You'll find EVERYTHING you want though. You walk into any club that's poppin (ex. The City) and hang by the bathroom and there will be a dude there with a bookbag and he will have EVERYTHING in there. Same thing with any resort that's on the beach. Chill on the beach for a little bit and someone with shyt will literally walk by.
Coke, Meth, Molly, any kind of pill you can think of. Cuban cigars. Anything.
But just know, the weed will be the most awful thing you've ever smoked. It is exactly as it looks, Mexican Brick weed.
Just bring a few carts with you man. Throw that shyt in your checked luggage. They ain't looking for no carts, they're looking for guns and explosives.
Some people sneak trees. I wouldn't recommend it. For every 100 people that sneak through with a zip, there's a least a few that get caught and you don't want those problems.