Why would you not seal the sack? Seriously. That is what I do with food if I know there are roaches in the neighborhood. Trust me, no roaches are getting in my food.
They're great huge sacks of rice - you can maybe fold over the top, but short of putting duct tape over it every time you need more rice, there's no sealing to do. I'm sure many people do that anyway, but I wouldn't trust many restaurants to, nor many shops.