An ideal all-purpose backup light might be the Blackburn 2'Fer. Not optimal for much of anything (although it's an ideal helmet light), it's small, lightweight and versatile. Red and white modes, flashing and steady.

Skip the supplied mount to save weight and bulk and stash it in a pocket. It'll clip onto a belt, backpack or shoulder bag strap, shirt collar, hat, saddlebag light strap, etc.

It's barely adequate as a to-see front light. It's a non-directional flood. I've used it that way a few times and it was adequate for getting home at 8-10 mph. Mostly it lit up reflective objects -- lane markers, cars, signs, animals -- just enough to navigate by carefully.

The 2'Fer is best as a to-be-seen helmet light. That's how I've used mine for a couple of years. It's also excellent for nighttime use lighting up the bike for repairs, flats, consulting a paper map, etc.

Only real shortcoming I can find is the 2'Fer doesn't run nearly as long or as bright as the Cygolite Hotshot 50. If Cygolite introduced a white/red flashing/steady version of a Hotshot I'd jump on it as an all around and backup light. But the Hotshot is a bit bulkier than the 2'Fer and not really pocket sized.

The price has come down since the $25 price for one in 2015, then $45/pair of 2'Fers in 2016. So I may grab another since I'm guessing Blackburn is about to discontinue the 2'Fer.

Or Blackburn may intend to continue the original 2'Fer and offer the brighter 2'Fer XL as an alternative. The 200 lumen front should be a bit better for navigating home in a pinch, although it's still a non-directional light.