I've also packed a duffle bag similar to the one Jen recommended & I use it for all my clothes (mostly dirty by end of trip) & check it on the way home. We usually check our carry-ons on the way home anyway.
I keep all valuable souvenirs in my backpack which is considered my personal item in the plane.
I usually only buy small souvenirs because I hate lugging around extra baggage.
On my most recent trip, I went to Europe to join my daughter who had spent a semester studying abroad, so she had a small-medium duffle bag with extra clothes. We ended up sending a package home because it was such a pain to have to carry this extra bag along with our roller suitcases.
Have a wonderful trip!