Providing leadership and keeping people working on something productive should keep panic at bay in many situations. But there are other situations where the panic could be beyond control. An example of this kind of situation is in the 2 nighclub fires last winter that resulted in a stampede for the front door and scores of people being trapped inside to die.

In a situation where panic is beyond control, about the best you can do is keep calm and lead the few remaining rational people that you can while abandoning the rest. Sometimes you can't save everyone and you have to set a realistic goal so you don't suffer the same fate as the mob.

But this kind of panic is not likely in your specific question of being in the woods longer than expected. In that case, effective leadership should be sufficient. Hopefully the group will have a leader beforehand, either formally or informally and that person will be in the best position to continue leading. Simply work through that person to keep the group doing the right things. Or maybe that person will transfer authority to you or someone else as appropriate.

If there is no leader, you have to decide if you will try to emerge as a leader or support someone else's emergence as a leader. This might be informal or done by taking a vote. Be prepared to explain why you are qualified to lead or to provide guidance to the leader on survival decisions.

In my experience, where there is no formal leader and people don't know each other beforehand, the process of designating a single leader is very problematic because you often have more than one person who simply will not be a follower, or the person exhibiting the most obvious alpha behaviour is unqualified for the situation. And this brings it's own kind of chaos. A vote might resolve the problem, but you may have to decide whether it will be better for you to work within the group or split off to save yourself and any that will follow you.