+1 for Magicshine – I love mine and it completely changed the way drivers treat me.
Also, agree with what others have said about lights and reflectors at different heights (helmet, arms, … ) – and it gives you some back-up if one of your main light fails because you forgot to charge the battery. And a class 2 hi-viz vest (cheaper and better than most of the specialist cycling ones – try eBay). It sounds like overkill and you’ll look like a dork, but really, really, never underestimate how much drivers are not seeing you. I’ve found the trails are usually well-enough lit, but it depends where you are, and last year the lights on the W&OD near the Route 66 crossing in Arlington were out for several weeks so the Magicshine came in useful there too.