009jim

Can anyone show me how I might mount a tail-light to the end of my flat bars. My hands grip all of the bar end, so it seems like it would need to come out of the inside hollow, maybe?

mechBgon

Here you go, the flat-bar variant of this one: https://bontrager.com/model/06988 They run on one AAA per side, so you can use rechargables. And that would be a good idea, because they do need fresh batteries every ~15 hours of use. Their weakness is the ribbed rubber sleeve that retains them in the bar, which can split after a while. You can get replacements for those from a Trek dealer if necessary.