Lots and lots of hides, until you can set up something better. Empty granola bar boxes, paper towel tubes, fake plants. Anything you have sitting around that can make him feel safe and that you can keep clean (or throw out when soiled) until you're able to upgrade. What kind of tank was he in at the apartment? Could he stay in that one? Also what kind of person abandons a live animal like that? I'm glad you're taking him in.