I would recommend these items: 1) Thudbuster, 2) a decent bell (stock one belongs on a tricycle), 3) Ergon grips, 4) Ibera RA5 rack, 5) pair of Ortlieb pannier bags, 6) Brooks B67 seat, 7) the more expensive headlight option that comes as part of the City Kit--my dealer got me just the light, no fenders or luggage rack from the City Kit and it's really good, 8) Shimano pedals and shoes with clips that really keep your feet on the pedals (sorry, don't know model #'s but got from REI), 9) Mirricycle rearview mirror, 10) mount of iPhone/cell phone so you can use Strava as you ride, 11) like others have said, batteries and more batteries.
I ride long rail to trails routes--like the 240 mile Katy Trail in Missouri. It's wonderful, but electrical outlets en route can be scarce. I have two gold batteries, one purple. With them, if I don't ride too fast which leads to great air resistance and drag, on fairly level ground I can get about 100 miles without having to recharge. Between the bike, panniers, all other accessories and me--at 220 lbs., that's pretty decent, though I take the charger and if I think I may run out of power, will try to find a place to rest up or have lunch and charge a battery while I am off the bike. That puts the load at about 300 lbs. I could use another battery but carrying a third one in the panniers adds a total of 20 lbs. of weight--a lot.