For at least the last 8 years, we've done vacation trips with one carry-on, and one backpack each. These trips included 2 RTW 2 month trips, with one of them with a China cruise within. Never a problem.
We travel with clothes that are easy to wash, whether by laundry of the bathroom sink. We wear our jackets so they don't need to be packed.
Haven't had any problems.
As for bringing back purchased items, some we shipped back.
One memorable experience when we were in China on a Viking cruise-flight-land tour: In Xian, everyone was enticed by the terracotta statuary souvenirs in museum shop. they weighed a few pounds, and were 1-2 feet tall. We saw people carrying those back to the ship, and on our flights.
As I had internet connectivity while in the shop, I googled the items, and was surprised to find the exact same items at Amazon. For less money, too. We simply ordered them online later from Amazon US, and since we were Prime members, free shipping.
So...that internet connectivity came in handy. Sometimes that unique souvenir just might be available online.