What can I do with like-new, recent-edition textbooks that I'm not allowed to sell? My employer is sponsoring most of the tuition and fees for my master's degree (in aerospace engineering), including required textbooks. Thus, it is unethical and against policy for me to sell those books once I'm done with the corresponding courses. Specifically, the policy is that I cannot "make a profit on" them, but other than that I am free to do with them as I please. I find that having the physical book is helpful when I'm taking the course, but afterwards if I need to reference it a digital copy will suffice. And while having my office/residence full of these high-level materials certainly makes me feel good about myself, it's not practical. Thus, what can I do with these textbooks that will have the biggest, most positive impact on academia?
Ask your employer.

You should be able to work out a solution both parties are happy with pretty easily. The obvious one is to sell the books and then give your employer the profits. If they don't care, you can also pocket the profits yourself, perhaps recycle the books or donate them to your university's library.