One other thing, when you are leaving the USA, your suitcases have to be checked in unlocked so that US Customs can open them if they want to. If they are locked they will open them anyway.
When we got home last summer, two of our cases had a note inside them saying that they had been opened by Customs.
HINT: if you don't want your case opened then it is a good idea not to bring back stacks of poker chips in your luggage. We had 5-6 ccases and the ones with the poker chips were the ones opened. Maybe they couldn't identify the spherical shaped objects from the x-ray. On the plus side I'm more than happy that they inspected anything that they regarded as suspicious.
Murt