We also do this, when we are Drinking Around the World (but most of the time, we do both over a couple of days, as we get just too full!) Here are a few tips:
1. Try to limit the sweet snacks - the sugar in the heat can really create a hang-over type feeling.
2. Have lots of water.
3. Enjoy the snacks that you might not regularly try, so you get the cultural experience that IS Epcot.
4. We like the inexpensive, personalized passports you can get online (google Showcase Snacking) to keep track of our snacks.
5. Keep photos of your excursion. Since it is an adult visit, maybe a kiss in front of a landmark in each country?
Favorite Snack options:
Mexico - probably something from the counter service to share, since these tend to be bigger;
Norway - Schoolhouse Bread (one of the sweet snacks I must have);
China - We like the potstickers;
Germany - A pretzel is a must;
Italy - This is where we go in the wine bar and sit for a bit - we love the meat and cheese platters;
US - Not my favorite snacking location, but we probably do the turkey leg most;
Morocco - The skewers are delicious;
Japan - Sushi, for sure;
France - Maybe a crepe?
UK - Scotch egg in Rose & Crown;
Canada - There is nothing available except popcorn, unless things have changed lately.
Envious that you have a trip coming up!