I don't have a favorite snack from each country but I do have a few "must haves" my traveling buddies and I always seem to enjoy!
American Adventure - Peach Cobbler (Liberty Tree)
China - Curry Chicken Pockets (Joy of Tea)
France - Napoleon (Les Halles)
Germany - Nudel Gratin (Sommerfest), Sea Salt Caramel (Karamel Kuche)
Italy - Cannoli (Tutto Gusto), Small Plates especially the Asparagus and the Seafood salad (Tutto Gusto)
Japan - Kakigori (Kabuki Cafe), Sushi (Katsura)
Morocco - Baklava (Tangierine Cafe Coffee Bar), Tapas especially the Brie, Fish Croquettes, Hummus and Spicy Shrimp, (Spice Road Table)
Norway - Troll Horn (Kringla Bakeri)
United Kingdom - Fish and Chips (Rose & Crown Pub, Yorkshire Fish Shop)