Index Cards
When the exams are going on, it does not take a long time for students to finish one pack of index cards. At the dollar store, a pack of a hundred cards will only set you back by 50 cents. If you prefer buying in bulk, you can also get 12 packs for $6.
Flashlight
Okay, they do not have the best quality. Even so, mini flashlights can be very handy if there is no power. They have keychain hooks as well, which makes them easy to bring with you. The price is also good!