I think bed sheets have been my biggest surprise. I would have never considered bringing sheets along...but even "higher end" bedding in every other country I've lived in has not been great (most of my time has been in Peru and Argentina...though Medellín is one of my favorite large cities).

Cold medicine is one thing I have to buy name brand for. For whatever reason Walmart versions of NyQuil has never worked for me, and neither has the stuff I find in most other countries. So I always stock up when in the US!