Blast from the past! I remember playing elastics with my sisters when I was in primary school and I loved introducing my own girls to the game.
What you need
Approximately 4 metres of thick elastic (at least 1.5 cm)
Three people (or use a chairs in the place of a person if needed)
The idea is to jump over different parts of the elastics (and sometimes on) in time to a riddle. Then increase the height of the elastic with each successful jump, from the ankles, to the the knees, and then waist, and even higher! There are many different riddles you can jump to, and you can find more ideas here: Elastic Game Riddles. The one I remember doing with my sisters is this:
England, Ireland, Scotland, Wales (1, 2, 1, 2)
Inside, Outside, Inside, Out
And so that is the one I taught to my girls. They loved it!