As these threads are usually fun when they get going, and both new folks and regulars to contribute!
Here are some of the earliest things I remember:
~Seeing America Sings and Tomorrowland at night and being a bit overwhelmed by basically, the awesomeness of it (the AstroJets spinning and the lighting and such)
~Having a Welch's frozen grape juice from Fantasyland then riding the Skyway
~Running around Tom Sawyer Island and being equally fascinated/frightened by the bottomless cavern and eerie noises inside Injun Joe's Cave
~Being freaked out by the cheesy sea serpent's gradual appearance aboard the Submarines.
~And as I am sure many here can relate to (those who visited before DCA was built), walking to the front entrance from the parking lot (Bambi section!) and being eager to get inside and start doing things.
How about you folks out there?