A pump, multi-tool, a patch kit, and a spare tube. A rear blinkie light for rides when the visibility is not so good, i.e. overcast or evenings. Water bottle and cage. I like the insulated ones. Depending what you plan to carry, a rack or under seat bag. That covers all the basics, just get out and ride. Later, you might decide you want a computer to track your mileage. Or narrower tires. Or wider tires. Or a different seat.