I am going to Canada, I have a valid U.S. tourist visa (B1/B2). Can I transit via a U.S. airport on the way to Canada with this visa? Logically I know I can since I am allowed to enter the U.S. but I am just making sure.
A B1/B2 visa is good to transit through US airports. I have asked an immigration officer in Dulles airport.
So I couldn't find the exact answer but you will need to fill an I-94 at the time you enter the US.
The I-94 states a couple things about your identity, but especially the customs officer will ask how long you stay in the US, what you will do and where you will stay. Whenever you enter the US, you had better know an address where you will stay. If you don't stay in the US (if you leave the country within the day) maybe you don't have to provide such information, but you can still prepare it in case.
Apart from that, I see no reason why you wouldn't enter the US (well unless you don't respect the law obviously). By the way don't bring food it's forbidden.
EDIT based on comments.