Aside from what was mentioned:
Water bottle, water bottle cage, Bike gloves, Sunglasses, tire pump, bike lock, tools (could buy a multi-tool which is what I did) I have the Crank Brothers multi-tool. Maybe a good spoke wrench if you'll use it, crank brothers came with one though I haven't used it yet. You might want a bike computer too.
Also, clipless pedals and bike shoes if you feel like it.
I just ordered a lot of this stuff myself but still have more to buy.too.