a couple Public Service billboards on freeways leading to some of the big park areas might be something for SAR groups to push for.
they have "do you know where your kid is" why not "are you ready to get lost?"..people of course zip by at 90MPH but it might jog a few people to put a few extra crunchy bars and that foil bag they see at the 7-11 check out into a pocket..