I've never been there, but I'd assume it would be similar to other afghan cities WRT food selection. If you are cooking for yourself, you should have access to a decent amount of fresh vegetables and fruits in markets, as well as rice and bulgar wheat for grains. Lamb/sheep, camel, chicken, and certain fish are the prevalent proteins in the arab diet, so I would assume you should be able to find those at a butcher as well.
I'm sure someone who has been there can provide some better info on where to go vs. not go - where is safe vs. unsafe.
On a positive note, cheating is going to be more difficult since fast food chains have been banned from Kandahar.
Br