As a U.S. citizen, what is required of you to walk back into the U.S. after a short visit. Is it inconvenient or do you just show your ID and walk across?

u.s passport is required but if you don' t have one they will accept an id and/or birth certificate but it will take longer without a passport

They can actually check your name in the computer as well, is helpful to have an ID of some type. I was always sent to secondary inspection without fail, but I also have criminal justice involvement.