US to Rome, security and bringing back items

If you're checking luggage you can bring back pretty much what you want as long as it fits it with the requirements of the US Customs and Border Protection. This page here details what is permissable and not: https://www.cbp.gov/travel/us-citizens/know-before-you-go/prohibited-and-restricted-items.

If you have carry on only then the amount of liquid allowed is the usual 100ml restriction.

On your return, you will collect your luggage in Atlanta to go through customs check and then recheck your bag(s) on to Charlotte. All liquids including oils and wine must remain in your checked bag(s) after any checks done by customs. You then go through security again (because you had access to your checked luggage and may now could have something with you not allowed on the plane) and are then just like on any domestic flight.

On your flight to Rome, you won't need to go through security again in Atlanta, if you've gone through security in Charlotte. On your way home, once you land in Atlanta, you will go through passport control first. If you've checked luggage, you will claim your luggage at a baggage carousel, then you will physically walk it through customs. Unless you're importing food, etc., you will walk through lane "nothing to declare." Then you will recheck your luggage and continue following signs to "connecting flights." All of this will be done INSIDE security. However, after you recheck your luggage in Atlanta (or not, if you just have carry on), you WILL have to go through security again on your way to your next flight. This means that EVERYTHING in your carry on luggage from Atlanta home to Charlotte will have to meet the TSA guidelines for carry on luggage, i.e., your 3/1/1 bag must be compliant, etc.. If you buy anything like olive oil, wine, hand lotions over 3 oz, etc., those DO have to go in a checked bag. Even if you purchase them in the Rome airport, inside Roman security, and the salespeople there tell you there that you can carry these items on (I've actually seen salespeople in the Rome airport do this), you CAN carry them on from Rome to Atlanta but you will LOSE them at TSA security in Atlanta if they are over 3 oz. and not in your 3/1/1 bag.

Sorry, but those sales people in the Rome airport are correct.
In 2014 the TSA rules changed. You can bring larger liquids in your carry-on for connecting US flights. They have to be sealed by the duty free shop in a secure see-through bag with the receipt. The bag cannot be opened or tampered with. The duty free shops know how to do this and TSA is aware so you shouldn’t have any problems.
These sealed bags do not have to be transferred to your checked luggage.

Thanks all! When I was in Venice 2 years ago, I saw a large number of people carrying-on those see-through duty-free bags with liquids over 3 oz for sure! I was wondering if those would get confiscated boarding the Charlotte plane. I'll be only using carry-on luggage but I wonder if I should bring an extra bag to store clothes and check in my main bag so I can bring home items over 3 oz.

The last 3 times when we have come back from Jamaica thru Charlotte we have had to place our TSA sealed bags in our checked luggage when you collect it after arrival. We have seen people throw away their sealed bags when they reach security.

The OP mentioned oil. One thing to note is that the liquids must be in a clear container, no metal or ceramic .
If you google it, there are lots of articles. The TSA also has the official policy on their liquids rules page in the section pertaining to international flights.
You could print that out if concerned.

I don’t know what happened on the Jamaica connections. My nephew connects frequently through Atlanta, always with bottles of wine in hand.
Have a good trip.