Help with purchasing textbooks?

I’m trying to purchase textbooks for my classes. I went on howdy-my schedule and clicked review/order books.
It shows 5 items for Biol 111 and 5 items for math 111.
Some are required and some are recommended. Do I just purchase the required ones? What do most students do? Order early, buy it on campus, or wait for classes to start (but I would think it would be too late by then)? Also, where is the best place to order them? From A&M, Amazon, or somewhere else?

Forgo to to add this in: What is the best format to buy? Ebook, used, or new?

@patstar5 - My son was a freshman last year in Engineering. He found that the posted book lists did not always match what the professor actually required on the first day of classes. Make sure that you can return anything you don’t really need. We also rented some of his textbooks from Amazon and bought others used from them.

FedEx and UPS will deliver to your room, but someone has to be there. If FedEx misses you, they will hold the package at their University Drive office, right next to Subway, which is pretty convenient. UPS is quite a walk from most of campus. (If you have a mailbox, then no worries - use that.)

In that case, should I just wait until classes start? I might be changing my science elective.
Do they have the books available on campus (though I am sure they will be much more expensive.)