Race Against Time
Source: Woodcraft Folk Games Games Games
Decide on a particular kind of race or activity that can be timed. One player completes one leg of the race, and their time is announced to the group. The group then has to guess how long it will take for the entire group to complete the race in relay fashion.
This can either be a group guess or individual guesses per player.
Part of the fun of this one is deciding on a suitably fun race/activity.