Not all jurisdictions will require tail lights on a bicycle after dark but a desire for self preservation should overrule and dictate that the bicycle traveler have decent lights on the bike to make them visible to motorists approaching from the rear.
We like the Spanninga fender mounted lights and the XLR Road Handlebar Plug Lights. For those who don’t have fenders (hard to imagine) or who don’t want to mount lights there, we like the B&M seat post mount battery lights.
The bar end plug light is a pretty clever idea that seems to work well.
I first saw these on a bike we were following on a rainy night in a suburb of Seattle and I was impressed with the extra visibilty they provided. They are friction fit inside the handlebar and run on two camera type batteries, which are included.