The US Customs and Border Patrol website has lots of information to help you understand what is and is not allowed. Make sure to read the specific sections for Canadians, too, as there are some exemptions to some of the rules that apply to everyone else.
Fresh products (meats, fruits, dairy, etc) are the big gotchas. Commercially packaged shelf-stable prepared foods in quantities that are reasonable for your family to consume are a safer bet, but again check against the CBP list.
Note: I have gone through US CBP pre-clearance with a fresh Swiss Chalet chicken meal from the airport restaurant. Although the CBP officer joked he might have to seize it so he could have lunch, he let me through once I promised I would be eating all of it before getting on the plane.
DECLARE ALL OF IT. In my experience, it adds the 30 seconds to a minute to clearing US CBP for them to ask what food and you to answer. Only once have I ever had it take longer, and that was coming back from a
Disney Cruise at Port Canaveral -- I declared the commercially packaged, still sealed, food we had (two boxes of tea from the UK pavillion at Epcot, and a bag of gingersnap cookies I had brought with me but not needed to open). The CBP officer had to get an agriculture-trained person to speak to us and clear us, which added another maybe two minutes.
The ag dogs have good noses. Declare
Finally, remember that the peanut butter is a "liquid/gel" and so the jar of it needs to travel in your checked baggage assuming it exceeds the size limit for the your carry-on 3-1-1 bag. Ditto jam and a long list of other things (including many food products) one might not consider a "liquid" or "gel", but which security screening does.
-SW
