Thanks for your help everyone. I do hope that I get a chance to go to the supermarket but if I don't I still want to be prepared.

So, if I bring my food in my checked luggage, not my carrying on, can I leave it in its orignal box? For example, if I bring 1 box of cheerios, 1 box of cornflakes, 1 box of cookies, 1 box of microwave popcorn, etc.

OR do I still have to empty each into clear bags? Or are the clear bags just for liquids put in the carry on bags?