This is one of my favorite topics! I love reading everyone else's first-day traditions because it makes me even more excited to get back.
We generally arrive around midday, and we always head straight to Epcot. The next part is somewhat negotiable. We ride a handful of rides, usually some combination of Spaceship Earth, Test Track, and The Seas with Nemo and Friends. Then, we get to our dinner reservation at Via Napoli, which isn't negotiable. It doesn't truly feel like we've arrived until we've eaten far too much pizza.