Vault

If you want to save a backup of a object, vault it. Then later you can unvault and select it to bring it back.

Vaulted objects are stored outside of the blend file as to not take up space and slow the machine.

For example, before applying a modifier like bevel or subdivision, run send to vault to store a copy without it being in the blend. Then later on if you want it back simply unvault it.