1. To replace a book you spilled wine on.
  2. You're drunk and you need to spend time somewhere before you go home.
  3. To buy a book you could get for $10 cheaper on Amazon.com but you don't want to wait for it to ship.
  4. You're at lunch with a guy and he's like "oh I have to go" and you're like "oh I have to walk that way anyway, I'm going to the bookstore" and then you walk that way and then you go to the bookstore.
  5. To read expensive magazines in the corner and then not buy them.
  6. To get coffee.
  7. To study.
  8. To look at books.
  9. To buy books, in general.