Keys and backups
Your Lightning node or wallet will have keys. Look at Backup for instructions.
Bitcoin key (on-chain)
Making backups is not easy. Probably just take your wallet-file... See github for more info.
Tip for now, just backup the whole ~/.lnd directory.
There is work underway to make backup better in 6.0: https://github.com/lightningnetwork/lnd/pull/1364
Commitment revocation private key
Every commitment transaction has a unique commitment revocation private-key value that allows the other peer to spend all outputs immediately: revealing this key is how old commitment transactions are revoked. To support revocation, each output of the commitment transaction refers to the commitment revocation public key.