Chubby, generally speaking most gear is sold over the counter in the US anyway -- they can't really be very concerned about you bringing in something you could readily buy once you're in the country. HOWEVER, you need to be aware that some gear is sold to LEO/Mil only, and some items aren't supposed to be exported, even though they get exported all the time anyway; that's the stuff that may cause you grief.
A vivid example right off the top of my head is IBAs (Point Blank's Interceptor Armor). While they are on the market, strictly speaking they shouldn't be even though you'll find them on eBay and stuff. (kinda like the situation in Canada with Issue CADPAT; on the books it says Don't Surplus, but it sometimes does get surplused anyway, and may also find "other means" of being liberated onto the open market)
Point in case, if the guy wants to be really anal about it, he could raise a stink about that (maybe he's ex military and hates you cuz you obviously aren't supporting the war in Iraq -- you know, being Canadian and all). There are some reported cases were the Marine Corp tracked down and re-gained possession of IBAs that had been sold to civilians.
So that's what I'd be looking out for.