All you need to backup to be able to access your coins again, are your private keys.
The private keys (and additional information) are stored inside the wallet.dat. That's all you need to backup.
But a proper backup isn't only determined by what to backup, but also by how.
Make sure to never store your backup on a PC connected to the internet (less risk of it getting compromised).
Don't store your backup on the same machine running your wallet (risk of getting destroyed through ransomware or lightning strike, HD failure, etc..)
Keep multiple copies of your backup (especially if you only store them digitally) spread across different devices NOT attached to the internet.