I used to cross the border all the time as an undergrad (graduated in 2002) without even having to show my driver's license...
Customs: "Where are you going?"
Me: "Casino/Toronto" on occasion, a friend would get bold enough and say "Downers"
Customs: "Go ahead"
in Feb 2004, I tried to cross the border (Peace Bridge) just to go to Peller Estates to buy some wine that my fiance really likes...I even brough my passport just in case since i wasn't sure what the border was going to be like...boy was it stevestojantty! they either had too much time on their hands (it was around 10am on a weekday so there was virtually no traffic) or the terror alert went up...anyhow, they pulled me over, took my new car into the garage and interogated me for a good hour...one question they kept bugging me about was how I could afford my car (2004 Subaru WRX Wagon)...they didn't believe me when I told them that NIH pays me pretty well to go to school...anyhow, since they had nothing on me and i guess they got tired of me, they let me go...went, bought my wine and left via the Lewiston bridge...shitstorm happened again...there was practically a blizzard at the time and were probably only 4 cars trying to get through and they pulled all of us over...again, my car got pulled into a garage and they did the same line of questioning..they went through my bag full of research, went through my files on my laptop (all school related research) and asked endless questions including "how'd you manage to afford this car?" over and over again...i was almost afraid they'd strip search me when they took my jacket and walked off with it...after an hour and a half maybe, they let me go...i spent more than 2 hours in customs that day
i haven't been back across the border since...i can only imagine how much worse my day could've been had I not brought my passport
it's not even like these were mean customs officials...they were all very friendly, but you have this very sick feeling in your stomach they you're going to get screwed anyway since they can do whatever they want to you as you have no rights in the no man's land