A worthwhile addition to your vehicle’s emergency kit and safer than incendiary flares, the small (6 oz. with batteries; 4 1/4″L × 3 7/8″W × 1″D) Lite Flare has a clear high-impact polycarbonate housing, two high-intensity red (yellow is available, also) LEDs that flash about 55 times per minute with a claimed visibility range of 1 mile at night, and uses two AA batteries that will operate for “400+ hours (alkaline type).” A 3-pack (the recommended number for “optimum” visibility) costs $33. They also make a Cone Flare version that fits in the top of a traffic cone to make it more visible.
If you don’t like the directionality of the Lite Flare, other manufacturers (e.g., PowerFlare) make LED flares that emit light in all directions.
I’m sure there are even more options out there. What do you prefer for road-side emergencies?