Inspections at the U.S. border are performed by the U.S. Customs and Border Protection Agency, in conjunction with the U.S. Department of Agricultural (USDA) and other government agencies. All have very strict rules regarding the importation of food, pets, medications and other personal items when entering the USA. If you are unsure what is allowed, make sure you check the U.S. Customs and Border Protection Agency website prior to traveling since regulations can be changed at any time.
Another website worth visiting is called EZBorder Crossing. Please be aware though that this is a "non-official" site, it's ownership is not disclosed and it contains some advertising.
But it does contain a wealth of helpful "crossing-the-border" information to make the process less stressful. Topics cover - The Inspection experience, working with the officer and what to expect . . . and some excellent tips to make your border experience easier for both driver and passengers.
The website also provides a separate page for every Canada/U.S. border crossing point, with much useful information.
As previously mentioned, this is not an official government site so any specific information it contains on what is or is not allowed should be checked for accuracy at the U.S. Customs and Border Protection agency website referenced above.