Sorry it took me a while to answer.
Fall back on means to have recourse to save you in case of an emergency.
For instance,
Whenever I can, I save some money from my pay. I think this is wise because I can have something to fall back on in case I lose my job.
or
Josh Brolin, supporting actor for Milk
"Don't do it, become a lawyer; have something to fall back on." —On his father's advice when he became an actor.
See?
See you next time.