Crop residues

Biomass waste refers to the parts of food crops that humans can't eat. This material is mostly fibre (cellulose).

Examples:

banana leaves
peanut shells
coconut shells
empty corn cobs with no kernels.
straw

Abundance:

Production is roughly equal to food production, because about half of the average food crop is biomass waste (the other half is food).
This page needs more precise numbers.

Uses:

All biomass waste can be burned for energy.
Some kinds of biomass waste can be converted into packaging.
Some kinds of biomass waste can be fed to ruminants (cows).
Some kinds of biomass waste can be used for cultivating mushrooms.
If there's no other use, biomass waste can be composted back into the soil.

3 and 4 are both ways to convert fiber into human-edible protein & calories. Help figure out which of these processes is more efficient overall. This page doesn't have enough information yet - join the discussion.