Obviously, had to get pedals.
Saddle was the first swap after < 100 miles.
Fork (the original one cracked) after ~ 2500 miles.
New wheels, tires, tubes shortly after.
Cassette + chain around 3000 miles but that's mostly due to mileage rather than wanting to upgrade.

I'm over 4000 miles now so I'm thinking of getting a cheaper CX bike to take most of my daily commuting miles and make those upgrades last longer.