I used a painted Ikea chalkboard to let people know what the plan was. I made medals from Reeces Peanut Butter Cups and York Peppermint Patties - I made a gold and silver for kids and adults for each race.
For game set-up, I spray painted a starting line onto the grass.
I used crepe paper, and green fence posts to set up a fun finish. I spray painted "FINISH" on the grass as well.
We did a three-legged race where people tied their ankles together. The older kids and adults all really got into this. After each race we awarded medals. We also did a kid's heat each time as well - they actually enjoyed this so much that we did more than one for most of the races.
We always make certain that there are things scattered about the lawn for kids to do: bubbles, an open sand-box, a bug net, a soccer ball, sidewalk chalk, airplane gliders, some ride on toys, etc.