How about urban aquaculture (fish farming). AFAIK the Romans started this tradition in Europe - with carp in fishponds. In medieval times every monastery, manor and castle had ponds, moats etcetera stocked with fish.
The modern version would be 'aquaponics' where you combine fish farming with hydroponics. This needs very little space and the plants live off the fish waste-products.
check out youtube for a small-scale version known as "barrel-ponics". It uses an electric pump - but presumably this could be replaced by a worker with a bucket, or the Roman technique of dams and sluice gates.
http://www.youtube.com/watch?v=FwMEulvJ2Ps
How about this scenario? In the T2K situation, indoor swimming pools become 'farming' assets for their town. The glass windows may have been shattered - but that just means raw material for the new (vegetable-growing) greenhouse while the old swimming pool is stocked with carp, trout or catfish.