?????
So this doesn't make sense. I'm not talking about only about the games I already own, I'm considering the games I will still buy in the future.
You can't buy games from one region in another. It doesn't matter where your Steam account is from, if you're connecting to your Brazillian account on the US Steam Store (because you have an American IP because you're in the united states), you'll access the US store and you won't be able to buy anything (because your account says you're from one country while you're accessing from another country).
You'd have, at that point, contact Steam support and let them know that you're traveling. Your account will then be unlocked to buy games from the region you're CURRENTLY IN.
In other words, while in the US, you'll be able to buy games from the US store, as long as you notify Steam support (and I would suggest you to contact the support BEFORE going to this other country and letting them know upfront). NOT the Brazilian store.
All in all, I'm glad I sold all these 21 TF2 keys earlier today, when the Russian-Store prices being adjusted rumour showed up.