Of course, it all depends on what you want to do with the bike, because, for example, if you never want to bother to work on it, you don't need tools, and if you don't plan on riding around more than your local environs, you don't need GPS.
That said, beyond the basic on-the-road-fix tool kit (tube, tire levers, multi-tool, mini-pump) which is handy for any bike and any ride that's more than a short walk from home or a bike shop, for road riding, I'd look at getting a seat bag to put the repair kit, ID, and sundry conveniences in, head and tail lights of some sort, gloves, 2 water bottles and cages, sport sunglasses for eye protection and comfort, chain lube (e.g. Prolink Gold, my favorite), a floor pump for inflating tires, a simple cycle computer with cadence sensor to display distance and speed and pedal RPMs, and some cycle-specific clothing, esp. padded bib shorts and a jersey, and toe clips for foot retention. If you have a smartphone, get the Strava app for recording, analyzing, setting goals, and having fun.
2nd tier importance would go to cycling shoes, clip less pedals (which means pedals that require a cleat to attach to the shoe, not pedals without toe clips!), a Garmin (or similar) GPS enabled cycle computer, and a bunch of other stuff that would be nice to have, but is too numerous to mention.
My last tip would be to watch some bike fix videos, presuming you no real experience with that. Don't need to watch a lot, just a few YouTube videos that cover things like flat repair, drivetrain adjustments, brake adjustment and basic maintenance, like cleaning and lubing.
That should get you a good way down the road... have fun, and ride well!