Bring as many boxes of "sandwich" bags that you can. All the way from the small ones up to gallon sized, or whatever you use. They sell them here in quantities of like 5 or 10 and are horribly expensive. I had brought down a number of boxes last time I was in the States but all but one box burned up in our kitchen fire at the beginning of the year, and I sorely miss them!
Tupperware or its like. Light and easy to pack and what's available here is crap.
Spices (there are only fairly basic spices available for the most part, none of what I list below):
- Seasoned Salt
- Old Bay
- Tony Chachere's
- Garlic salt (used to find this here, but haven't seen it in years)
- Chili Powder
- Specialty spices like McCormick's Grill Mates
- Anything you depend on for cooking that is dry and easy to bring and isn't salt, garlic or black pepper (although the latter can actually be difficult to find at times!)
If you depend on Crisco for pie crusts, bring a ton of Crisco bricks

Lard is not a very good substitute if you make pie crusts like my mom
I second good kitchen utensils, particularly sauce pans, good frying pans, woks, etc. You can get decent knives here if you look and pay a lot, but if you can bring them do so. What is available here is mostly terrible and costly and what's not terrible is more costly and there is not a good selection anyway.
I second, also, electronics such as cell phones, computers, routers and such. Appliances not so much - they're expensive here, but as mentioned, the power requirements make things complicated. I've never actually seen an actual clothes dryer here, in reality (though I've seen them advertised), but I rmember recently someone asking about bringing an electric dryer and it being complicated due to the electricity requirements.
If you are a physical book person, bring books. For the most part English books here have terrible selections unless you like cheesy romance novels or others (I'm not knocking it, but it could get boring). But for me the best thing to do is make sure you have some form of electronic reader (see electronics above) that can read the Kindle format and an Amazon account. I have Amazon Prime and can read up to 10 books at a time for free! (as long as the book is part of the program).
Clothes, clothes, clothes. Clothes here are terribly expensive. Inexpensive clothes usually don't last but a couple of washes unless you are extraordinarily careful (my wife and our girls hand wash a lot of stuff they buy here). Expensive clothes are not very good either. Very, very expensive clothes are OK, but are very, very expensive. If you are bigger-sized than normal, you will have a hard time finding clothes that are comfortable. And I'm not talking exaggeratedly big either - I'm a bit overweight, though not fat by any means, but I like loose-fitting clothes. An XXL shirt here, for me, barely fits (fits like an XL, which doesn't give me much space) - Latinos seem to like tight-fitting clothes and their sizes are adjusted accordingly. I still have clothes that I brought with me 10 years ago when I first came here, but only one or two shirts I've bought here over time. Shoes, especially women's, are horrendously expensive. Non-cheap-looking men's suits go for about 10000-12000 pesos (650 - 800 dollars - seems expensive to me, but I haven't bought a suit, here or in the US, since 2001).
Bags and suitcases and such are horribly expensive.
I don't know about K-cups here. We got into the coffee machine stuff while here and bought a Nespresso a year or two ago. A bit expensive but good support.