The local used bookstore here bases credit on genre type. So if you have $15 credit from returning romance novels that credit is only good for purchasing romance novels.
I personally am a fan of 2 local annual book sales. I always walk out with more than enough books for the next year. And at 50 cents for paperbacks and only $2 to fill a whole bag on the last day of the sale I cannot beat the price.
Library ladies with late charges: our library gives you a little print out like an adding machine tape. I post this right on my fridge so I see it each time I open the door. It's a constant reminder to return my books.
All that said I'm just about to start Dead to the World (book 4 in the Sookie Stackhouse series). Love these books. Even with taking classes at college this summer I have managed to read 3 of these books (and watch seasons 1 and 2 of True Blood)in the past five weeks. All while keeping up with homework.