Most people think of a backup only when they really need it. Be one of the people that think about backups before you need them. Best case scenario is to have a full backup ready, that includes your database and all files, to rollback to at any given time.
What does your individual WordPress consist of?
Your WordPress installation is your custom installation because of:
its database and
its /wp-content/ folder
If you have a backup of both you are set.