It really depends on how many you have. If you have a decent group (around 8 or more) a good game or two of capture the flag sure kills the time. If you have less then there is fire starting (making it a challenge), having them cook dinner or set up camp, or just kicking them out of camp to explore. Believe it or not, teenagers are big enough to explore without adult supervision. If you have boys of any age (teenager or younger) throwing rocks or sticks is always fun. Girls might or might not go for that, though. Then there is climbing rocks and trees. My scouts like to play this game called Ninja Strike. I don't really know the rules, but it keeps them entertained. I would say that teenagers are old enough and smart enough to come up with something to entertain themselves. I wouldn't worry about it too much.
_________________________
I've taken a vow of poverty. To annoy me, send money.