We take our trailer back and forth several times each year and my wife works in Detroit, commuting several times each week.
It is wise (but not mandatory at this point) to get a passport. They are good for five years.
You need at least three pieces of ID, one with a picture. A birth certificate, drivers licence, certificate of citizenship, work photo ID, etc. are good. You definitely need to be able to offer proof of citizenship. For children, a birth certificate and any other ID you have. And you may need to prove the kids are yours. So if you have someone elses children, you need a letter of permission from the parents showing the purpose of their trip, the name, address and phone number of the parents. Both sides are concerned about child abductions.
Leave firearms (if hunting check with customs on both sides re procedures) at home as well as any fresh produce and meat. While not all meat and produce is prohibited, some are and it is just worth the hassle of figuring it out. Leave ALL beef product at home. Neither country allows beef to cross the border and that includes ANY beef in pet foods, or any food with beef as an ingredient. Even the canned stuff.
You can take across one bottle of wine or liquor, or a case of beer per person of drinking age.
Pets need proof of current rabies vaccination (within the past year) and need to look healthy.
In short, carry proper ID and buy your food at the destination. Be courteous to the customes officer and answer all questions truthfully. And that goes for both directions. We have never had a problem EVER crossing the border. It really is no big deal. Both Canada and the US welcome visitors from the other. Let's face it, tourism is good for the economy and even the customs guys know that.
Casey