I put wet clothes in some. In others I collect sand or shells if the beach I am going to allows this. I also use them to pack sandwiches and chips that I ordered from Room Service to carry off ship. I also use them to put my cameras in when I am on shore, especially if they are not water resistant and you are anywhere near the water.
I also make up post card labels that I print on laser labels, so that when I am ready to do my postcards, all i have to do is slap the label on the postcard, and write a couple of lines.
gee, i know i have used them for lots of other things. I pack liquid items in these too, in case they should leak during travel.