I hope you got a helmet.After that it kind of depends on what you want to do. In no particular order.
I can't stand to not have mileage and HR data for my log, so for me that was an essential purchase.
Water bottles and cages
Clipless pedals
Tubes and a pump, some tools, a bag
Lights if you plan to be out after dark or could get caught after dark.
Gloves
Happy riding!
V.