/sci/ - Science & Math

Algae is a good source of food as well with many of the nutrients and vitamins people need and it doesn't require much to grow, the biggest problem would ofcourse be to set-up a place to grow the stuff in sufficient amounts. Some mushrooms however would be easier to do, nice source of nutrition and a good chance to recycle some waste material without much equipment.

And if all else fails, you'll always have a healthy supply of fresh humans.