Magazine subscriptions are allowed. Books from sources like Amazon and Ebay are usually acceptable if the prison allows delivery by sources other than the US Mail. A lot of prisons will not accept UPS or Fedex so be sure if you plan on sending a book, it's shipped through an approved source. Good luck.
Oh, remember that any magazine you send CAN NOT show nudity, weapons, drugs, ganglife or promote racial discord. I know you probably wouldn't do that but, I thought I'd let you know. Some prisons won't let pictures of tattoos come in even if they are in a magazine.