When riding after dark you really want some good marker lights for your bike. (A market light is a blinky light that *helps* drivers see you when riding at night.) I find, though, that most of these lights are either too big, or they use short-lasting and hard-to-find watch-type batteries.
But more and more companies are making USB rechargeable lights. Knog in particular makes a great series of surprisingly bright LED lights for your bike in soft silicone that recharge in any USB plug. This also means that you don’t have yet another wall wort to lose, and you can always do a last minute charge at work or even in the car.
These lights are also low profile and light enough to just leave on your bike so they are always there when you need them.