I would consider a dynamo system. Doesn't need to cost a fortune for something serviceable and it is fit and forget and will always be there when you need it. Drag is barely noticeable if the dynamo is fitted corrected (there will be a whirring noise though) and halogen light is bright. Can be made even brighter if you fit a 3w bulb and use a battery tail lamp.
You will need two cheap LED lights to supplement it when stopped or else spend more and get lamps with stand lamps.
You will need two cheap LED lights to supplement it when stopped or else spend more and get lamps with stand lamps.