For us, it is a variety of categories. Sometimes we bring back just memories. But, when things are brought back, they are small, packable and useful.
Small painting from Paris (it was more expensive to have it framed than the cost of the painting, since standard canvases there don't match the pre-made frames in the US), but we love it,
Christmas ornaments if I love the ornament.......and there should be a law against owning as many ornaments as we do.....two days to put them all on the tree/two days to take down and pack them all. Disclaimer: we did not put up the tree this past year, as we had no guests coming....sometimes one just has to give themselves a "pass"
Scarves - especially if one is found at a very good price. My 5-euro street scarf from Florence gets compliments every time I wear it (it could pass for a $200 scarf from a high-end boutique), but I always am straight forward about my great bargain.
Books, if special (like the book about the SeaCloud, purchased on board, signed by the Captain with the dates of the journey), and a book about fairy rings in Ireland that a driver we hired kindly gave to my husband when he expressed an interest in them.
Maps (such as the large nautical marked-up map from our small ship cruise to New Zealand and Australia, also signed/dated by the captain. We just happened to very casually ask what they do with the maps after the journey, and bingo we were surprised & delighted when a staff member later surprised us with his kind follow-up :),
Ballcaps are also winners for us, especially if they are of a nice quality and serve as a subtle brag item for my spouse to wear at home or on future travels .... he loves his Antarctica one and when people ask "Have you been there?"
Polar jacket from National Geographic trip...it's amazing how others that have gone on those journeys recognize "the jackets" in Kroger on super cold days...good conversation starters with other world travelers)
Sometimes a special liquor (ice wine from Eastern Canada)
Hand-crafted jewelry item (love my white porcelain/clay-like polar bear pin from Alaska with a red ribbon....Christmas favorite and gets lots of compliments each year)
Something we will NEVER do again (two cartons of fresh (de-headed/gutted) salmon we caught on a fishing trip in Alaska).......we were up until 1 am cutting and packing the night we arrived home. Lots of Salmon dinners with friends that summer (and I personally don't eat fish!!!)
What I am glad I CAN'T bring back home: Live plants.......oh how tempted I would otherwise be :)
What I just could not bring myself to buy its own plane seat for: A life-sized wool sheep that I fell in love with at a flower shop off Key Street in Galway. But, he sure was cute. Sometimes practicality does save me from myself :) :) :) He really was cute!!!!