I agree that this is a GREAT thread. Interestingly, just last Friday my four-year-old son suggested making "survival kits" for himself and his siblings (ages 6 years, 2 years, and 6 months). Part of it is that he'd seen me make a rather involved kit for my dad, as a Christmas present.
I ended up agreeing (though the 6-monther doesn't get his own kit yet.) Part of it is simply that I knew the kids would love it--and the other, more serious part is that I knew they'd feel motivated to carry their kits whenever they go outdoors. Part of this is the fact that teaching them this stuff is one of the main ways they and I enjoy spending time together on my days off. Another is that I can keep adding things to each kid's kit as they get older and more capable.
Thus far the kits are pretty minimal--little fanny-packs, festooned with blaze orange duct tape, with whistles, bright bandanas, and blaze orange knit caps. One note about the whistles: I recommend that you have the kid in question actually test out the whistle you propose for them to use. My two-year-old can't manage more than a feeble "pfft" out of a Fox 40 Micro, much less a useful "TWEET". I plan to see if a Storm whistle will do the trick. Obviously, I have no intention of letting her get out of sight--but I want to prepare against that possibility. I'm drilling all of them in the "stay put and whistle" procedure.
The 6- and 4-year-old I'm teaching more advanced stuff, though they're not yet to the point where I'd want to rely on their ability to use it. I've had them help me gather sticks for fire-building, and each of them has started family cooking fires with a metal match. I've got to weigh, in this, the chances that such skills may be misused--and, at this point, both knives and firemaking implements are staying out of their kits; in our dry Arizona, I'm worried they'd incinerate a whole county if they built a fire before really learning the ropes. Some of it will depend on the individual child: my 6-year-old is cautious to a fault, while I have the feeling that the 4-year-old would stand on the car hood at 65 miles per hour, collecting bugs on his teeth with a wide smile, if given the opportunity. The 6-year-old may thus get the opportunity to use firemaking stuff sooner. I've already had them help build lean-to shelters (their clubhouse in the backyard is a lean-to we built a couple of weeks ago), and I'm constantly encouraging them to notice constellations for navigation, where the water-birds are flying, and things like that. When I cut myself with a saw last summer, I involved the 6-year-old in the first aid procedure, explaining to him that there was no cause for panic, and walking him through each step as I cleaned and dressed the lacerations.
More ideas, anyone? Keep 'em coming!