For those who are health conscious there are many very cheap foods that are packed with nutrients. Dump the very expensive and overrated goji berries and chia seeds for the humble raspberry or linseed.
Stinging nettle. It's like spinach, but free. and those are abundant. You can also eat the seeds. Just be careful where to harvest. Harvesting near roads and agriculture areas is not a good idea.
If eating it yourself sounds scary, giving nettle tea to your plants is one other good thing to do.