My boys have quite a few of those certificates. When they were young I took them to all the character bfsts and they were given the certificate as they left.
The characters all "signed" the certificate in advance, in different colors all around the certificate.
They also have certificates from when they were chosen to participate in different shows at the parks. My middle son Sean had something, I don't know whay, but he got picked for every show at both WDW and the "other park". It made the other two so angry.
My boys also attended all the educational programs when we stayed on the "Food and Fun" program. that program included all three meals (sit down, appetizer, main course, dessert and drink) anywhere in the parks and resorts, and any "fun" which included all the boats, all the classes, and water parks. I think Disney lost money on us, we took the boats out 2 hours a day, and took all the classes. My sons had steak and eggs for bfst, we went to all the character meals, Coral Reef, Hoop De Doo, etc...
I have their "cells" that they painted in the art classes, photos they took with the cameras Disney provided at their Discovery Island Tour, and all the certificates that go along with them.
We also have some of the great books they provided for the Discovery Island Classes.
I took all the tours at Epcot during those years, all the "plantings of Epcot" etc. While they were in classes I got to take some too.
But Sean says his best experience in FL was when he was chosen at that "other park" to be slimed. We have a certificate for that too. Peggie