LED lights don't get much more basic than this, but simplicity really works in Raleigh's favour.
Sitting up front is a 1W LED that gives a small patch of light a few metres up the trail. It's not enough to ride hard by, but it's better than nothing if your main lights fail unexpectedly. There's a flashing setting too, which is ideal for startling drivers into noticing you.
Attachment is with a simple but secure rubber band and a 'flip over' lever mount that'll fit on standard or oversized bars. The plastic body holds the removable cell for four AA batteries and it's balanced well enough that it doesn't bounce all over the place. Output does eventually fade as the batteries dwindle, but stick in some decent rechargeables and you'll boost the long-term value.
It's all weather sealed with O rings, and it's proved a very durable 'just in case' carry along for several months now. There's even an alloybodied option for £25 if you want to get a bit fancy.