It is possible to feed chickens without commercial feed. It does require a bit of planning. As much as chickens like scraps, in nature the food chain indicates that bugs are between plants and birds in general. It's often forgotten.

I would suggest keeping some mealworms (or a native relative). It is a great source of nutrients besides protein and a whole bunch of them can live off veggie scraps for a long time. Many sources on the internet (even research documents) give wrong information about them, keep the humidity low, not high or you will accumulate pests over time.
They can survive freezing temperatures also. You can set it up with minimal input.