All of the programs listed above offer background material, including information about subjects taught, games played, and rules enforced. Class preparation should involve discussions about what exactly living history is and how it works. Your students need to understand that they will be pretending to be in a certain time period and must work at knowing nothing about events or items past of a more recent vintage. Part of this includes being dressed appropriately. A good source for period clothing is Children's Costume in America 1607-1910 by Estelle Ansley Worrell.
Lunch is also important.
The most authentic lunches would be leftovers wrapped in paper and a tin cup. Try to restrict soft drinks, potato chips, plastic bags, etc. Stressing these fundamental aspects of life will give students a better feel for history than if they bring modern victuals with them. To get maximum benefit from the living history experience the students must be well-prepared. They must know how to role play and have some idea of the historical time frame.