Most Crucial Gear/ Accessories for a (Road) Cycling Beginner?
Sounds like you have the basics covered pretty well.... If you're turning in some serious mileage, you want to be able to handle flats and minor repairs on the road.
Minimum is a good frame pump ( a lot of the mini pumps have trouble getting past 50 pounds or so...) spare tube, tire tools, etc.  Some of the handy little hand-cleaning wipes are a good idea as well.
A multi-tool that will take care of most emergencies is a good investment; it should include a chain breaker, allen wrenches to fit the fasteners on your bike, etc.
Some money is never a bad idea.  You may just HAVE to have a donut....