Hi. I live in Mexico and travel back and forth to the U.S. I don't like the food they have over here...well, my baby doesn't. The best brand I found was Royal Canin and my baby didn't like. Other than that, I have seen Eukanuba, Diamond, Science Diet and pretty much all the grocery store brands. The first 3 I found at a pet store in Guadalajara. I brought food for my puppy from the U.S. into Mexico. They didn't ask me if I had food and I didn't mention it. I had the bags in a box along with her car seat and when they asked me what was in the box I said it was a dog car seat and they kind of laughed at me.
But whenever I go to the U.S. I already tell the customs agent that I have a little bit of food (usually in a very small container) that I show them. They usually say that I can hold on to that small amount for the day, but whatever my baby doesn't finish, I have to throw down a garbage disposal. Even though the food is originally from the U.S.

I usually leave food for my baby at my parent's house, so that little container is just for the airport, in case she gets a bit hungry (which she never does).