My knee-jerk reaction to this was "my kids will always have a glow stick with them, everywhere, everyday, no matter what!" Which probably isn't the most practical choice. This probably sprang from my own experiences with losing people in the woods.
About 8 years ago, my youth group went for a day hike up the canyon near our home. In the course of hiking up to a waterfall, having lunch, and coming back down for a campfire, my sisters and one of their friends wandered off the trail and got lost. I still remember watching some of the grownups start to panic, and the fear was infectious. Luckily, my father was able to calm everyone down, organize search parties, and in about 2 hours they were found. Most stories like this from the area don't have such a happy ending.
One thing that my family learned from my sisters getting lost was the importance of having a whistle with you. They decided to sit down and yell for help, and quickly went hoarse and lost their voices. If they had a whistle with them, they could have kept up the racket indefinitely, making it much easier to Replace them. Whistles can be very inexpensive, but can make all the difference. They even have lightsticks that have a whistle built into them. These do have batteries, which makes them slightly less than ideal for the gas leak problem. But they are great because they come with a lanyard to hang them around your neck, have 200 hours of battery life, a whistle, and a small watertight compartment for matches.
So don't overreact, but don't let something that is so simple to do pass you by. What are some other, super simple, inexpensive must-haves for camping and emergencies?