My biggest gripe about the show is that the people know they have 21 days to survive.
So basically if they can start a fire, secure some water, and eat a few bugs from time to time, they'll make it. Since they each get to bring 1 item, that should be pretty simple to accomplish.
Things I would change:
1) Add more people. At least 12, 9 men, 3 women. You'll end up making the guys more competitive and also making outsiders of a couple of them.
2) Don't give them a finish date. Or if you do, tell them it will be years.
3) Make sure it's in a location that has enough resources they can actually survive with hard work and ingenuity.
I would hope for a total Lord of the Flies situation.