Scran is the most common name for the self heating ration packs that can be produced by large machines called Protein Spinnners. They are the default foodstuff of raider crews and are safe and nutritious.
Having enough spare Scran means that your band is no longer scrabbling just to keep its members fed. This gives you a big edge over competing Bands.
A Protein Spinnners can produce a portion of Scran from its own store of raw materials if it can be powered by 5 Cells. Alternatively, if you can provide it with enough raw protein from local wildlife, it can spin Scran using only a single Cell.
Protein Spinnners seem to be able to recognise human flesh and will reject it as a raw material. Although there are stories of cannibal gangs that have managed to over-ride those safety protocols.