Don't know where you're located or where you might tour in the future. Some places legally require both a rear lamp and a reflector, as does the Vienna International Convention on Road Traffic (1968).
I use a CatEye Reflex Auto
combined rear lamp and reflector. I power it with rechargeable AAA Panasonic Eneloops locally and can snag AAAs easily enough on longer tours. You would additionally need CatEye's
5445620 rack bracket.
