I like having a rear blinky on during all of my rides, night or day, unless I'm in a group in which case I leave it at home. Weight is negligible and if it helps one driver see me a tiny bit sooner and maybe keep them from running me into a curb, it's worth the AAA batteries I have to swap every couple months. I use a planet bike superflash, cheap but seems bright enough.

I have a cygolite metro headlgiht I use for dusk, dawn, or night rides. It wouldn't be enough for a pitch black singletrack ride, but it's perfect for roads you're already familiar with and has an easy handlebar mount. Wouldn't ever bring it during a normal daylight ride, though.