Using a 1T sack vary the number of people in a team for races.
2 or more 1T sacks, preferably unused.
Get the teams towork together to jump the sack from one lineto another, they will fall over and struggle until they learn to work as a team.
Start with 4 then 3 then 2 in each bag, seeing how they learn and get better. The race can have obstacles to go around.
Best done on grassed areas to ensure it is safe when they fall over.