When i go to the US , i make sure i pay a visit to Wallgreens a day before my departure to get my salad dressings , candies, spices , barbecue sauces . i remember vividly the appalled look on the Airport custom's lady face when she realized a
french guy was bringing "Velveta Cheese" back to France..(but it is the secret ingredient to Patti la Belle's Mac and Cheese!!)
When i go to London , i always stop at Sainsburry for my lemon curd , crumpets and scones
a supermarket abroad is an experience cause it tells a whole lot of the ordinary culinary habits of the country .
I encourage you to check out supermarkets a day before your departure . One has to be extra carefull with the packaging .
Here is a short list of the cool supermarkets from the most expensive to the regular price
take a look : http://www.lagrandeepicerie.com/en.html