My current mentor, Ms. Massey, a 4th grade teacher has been having difficulty with preserving her supply of all of her pencils and erasers. She bought 20 pencils and 20 erasers for the class. She left them each in their own separate buckets. Within a few weeks, they all just disappeared. Reasonably, she's discouraged from buying 20 more pencils and erasers because she doesn't want the same thing to happen to her.
This is what we do at Adventure Time (i.e. the before/after-school program) at Chabot Elementary for pencils and erasers. The rule is that if a student wants to borrow a pencil, they need to leave us their shoe. We just leave their shoe in a bucket. The shoe serves as the collateral. They can have their shoe back once they return the pencil or eraser.
If you want to use that idea, you just want to make sure that everyone wears socks to school and they stay in one spot while using their pencil. If for whatever reason, they need to walk around, then they shouldn't have any reason to have a pencil. In which case, you can take your pencil back and give them back their shoe.
Even the kindergartners never forget to come back to get their shoe. It's kind of hard to forget when every step you take makes half your body sink a little deeper for every other step. That and they'll obviously feel the difference on the surface of their feet.
Let's say that you don't want to say leave a shoe and borrow a pencil. Ok. That's up to you, but in that case, come up with some different idea for a collateral. The idea is that you want to come up with something that every student values that they won't want to leave the room without. If you can come up with that, then that can be your collateral. A shoe is one example of that. Either way, I wish you the best in preserving your pencil and eraser supply. Ours collection is actually building up.