After buying my bike I only made a few purchaces. The first was a helmet (never wear it).
Next was a pair of LED safety lights (Great purchase)
I bought a reflective vest (Another great purchase)
Urban tires for my daily rider MTB (Better speed/Nice ride)
Rear view Mirror (Best purchase ever for a bike)
Recent purchases are combined for a "just in case" scenario since I ride longer trips now..............
Seat bag (All items below go in bag)
Patch kit
CO2 can
Spare tube
Tire levers
Tools
Bike lock