Cool thread idea.
I stock groceries for work, so I don't really need a backup light, but I do commute to work on a bike and get home around midnight, so....
Work--------------Nitecore NDI in a holster next to my boxcutter. No backup
Biking to work----- A single NDI in strobe mode aimed at windsheilds. the backup is my other NDI
Biking from work----Dual NDI. A handlebar mounted Q5 pointing ahead about 20ft, and a GDP version mounted on the fork right above the axle aimed at the ground about 10ft ahead. I don't feel a need for a backup with two well made lights, but I do take 4 extra charged 2450mah energizers in my pack. Cool thing about having dual lights, when I get close to a busy intersection or any dangerous situation, I quickly turn the NDI next to my grips into strobe mode and just as easily turn it back to normal mode.
Out and about-----An NDI with the backup being a Fenix eo1
Anytime I leave the house for more than a day, I bring both NDI's. After all, someone once said on a gun forum, "The best backup you can have is the exact same model of ______ that gets the same ammount of use as the other" I wish I knew who coined that wisdom....:thinking: