Your kids, family, friends, etc. When I look back on the video we took 10 years ago, I skip through the parades, shows, etc and spend most of my time on the shots of the people I was with.
If you are traveling with kids:
1) Video your kids playing.
2) Engage your kids in conversation and record what they have to say. On my next vacation, I intend to shoot some conversation with the kids every day about what we just did and what we are doing next.
3) Shoot parts of the big events like Spectromagic, Fantasmic!, Illuminations, Wishes, FotLK, etc, but don't shoot the entire thing.
4) Record setup shots. For example, record a bit of the entrance of each park as a setup so that viewers know when they have changed parks.
5) Record the things that are special to you. That might be the desserts you eat, the characters you meet, some rides that thrill you, or just a little spot that you like to relax in. Whatever you think you'll want to remember 20 years from now is what you should record.