From inside the city and the attacking force there is always bound to be food ripe for the taking but that isn't necessarily my department with theft. Con men can do some but all the thieves are on the day shift. It's as Bronn says in Game of Thrones thieves love a siege. Money, money, money.. Cause no offense intedend men can become preoccupied by a beautiful woman which would by us the time and means to get the food. Regardless though, everyone is on a double edged sword. The only one not affected to much by the is the Merc captain as he could very well pull a trick and just let them  pour in the city. To me I think honestly that where the power resides.