(In no particular order) fresh milk, fresh eggs, Cadbury chocolate mini-eggs (only available around Easter), decent selection of beer and wine, high-quality beef, Chipotle (yes I like to indulge in a 1500 calorie burrito every now and then), lemons, asparagus.
Overall, I don't really miss much in the way of packaged products...it's the quality fresh food. I just miss having access to places like Wegman's and Whole Foods. Whenever I'm in the States and go into a Wegman's I almost cry. So much amazing produce and meats. And the prices are amazing.