What are some games you can play in the middle of nature and a bunch of people?
There are the classic games you can always play, like tag, or I spy, or Truth or Dare, but there are plenty of ways to be more creative.

You can collect a bunch of rocks. Then about 10 feet away create a small stack of rocks. Each person takes turns with their own pebbles and tries to knock the stack of rocks over.

If you are near moving water, you can have a "stick boat" race. Everyone chooses a stick and places it at one point in the river, and you cheer and goad each other to see who's stick wins the race.

You can divide into teams and create "nature art" like Andy Goldsworthy who assembles leaves and sticks into beautiful images.

You can simulate games like Bocce or Frisbee Golf with things you find; rocks can be bocce balls, sticks can be frisbees.

You can make a game out of anything.