Locate the Shipping area early and set up a box (provided by the folks who run the shipping area). Find a space on the one of the many tables, borrow a marker and label your box. Then whenever your tote bag gets heavy, you can offload books to your box and go back out to collect more. But collect galleys judiciously; it’s very expensive to ship from the Convention Center. Keep in mind that many are available through Edelweiss and Netgalley.