Although this post is old now, I’ll still enter my ideas (good or bad) before reading the other comments...
Video games. Expertise in one video game is not good enough; ideally, speed rationality of 100 people could be tested on a new game none of them had seen before.
Along similar lines, ask the 100 people to cooperate in a large artificial project which requires that number of people, such as the manufacture of a complicated item invented for the day. It should be complex enough that cooperation is needed; IE, involve several complex skills such as a specific (ideally new, or new to the group) origami folding. Each individual is scored on how many of the item they have in their possession by the end of the day. It would be possible to work alone, but more efficient to work in groups and split profits. (Ideally the item is complex enough to encourage very large groups, tending towards everyone needing to work together.) This has the additional benefit of being a good learning experience.
Although this post is old now, I’ll still enter my ideas (good or bad) before reading the other comments...
Video games. Expertise in one video game is not good enough; ideally, speed rationality of 100 people could be tested on a new game none of them had seen before.
Along similar lines, ask the 100 people to cooperate in a large artificial project which requires that number of people, such as the manufacture of a complicated item invented for the day. It should be complex enough that cooperation is needed; IE, involve several complex skills such as a specific (ideally new, or new to the group) origami folding. Each individual is scored on how many of the item they have in their possession by the end of the day. It would be possible to work alone, but more efficient to work in groups and split profits. (Ideally the item is complex enough to encourage very large groups, tending towards everyone needing to work together.) This has the additional benefit of being a good learning experience.