Not sure if they still have it, but Kidcot was fun for our kids. They could get stamps and make a craft in each of the WS countries. They also enjoyed talking to the cast members from the different countries.
Although I haven't done it yet, but plan to in June, you can do the Kim Possible adventure.
I agree with other posters that you must do Soarin'. It's one of my top 3 favorites at WDW.
I enjoy hitting Germany on the hour to see the clock display.
We also enjoy some of the bands in WS, especially at Canada and England.
Watch the Fountain of Nations.
American Adventure should not be missed.
For shopping, it's fun to visit the department store at the Japan pavilion. Also, watch the rice candy being made into animals.
For eating, we enjoy the pastries at Norway (School Bread!!) and at France (Coconut maroon or Napoleon), or the Kaki Gori frozen ice at Japan.
I haven't tried it yet, but I read recently about Grey Goose or Grand Marnier slushees at France. One of those is on my "must try" list for our next visit.
If you really want to pig out, take a walk from the World Showcase entrance and go over to Beaches and Cream at the Beach Club and get the Kitchen Sink.
ETA: Stop at the Imagination Institute and make your own virtual postcard. These can be quite funny especially with the morphing. You can also explore some of the exhibits.
Also, I recommend taking a break and riding the monorail to the TTA. Once there, get back in line to take the monorail back to Epcot but ask to sit upfront. Only four can sit up front, but you can get a great view of Epcot when you come back and go through Futureworld sitting in the front of the monorail.