going back to sleep; sleeping in
again and again; repeatedly
double take (esp. out of surprise)
what happens twice will happen thrice
double-dipping (a food item in sauce)
getting two pleasures from one thing; two benefits for the price of one; having one's cake and eating it too; delicious in two ways at once
you are only young once; youth doesn't come twice; gather ye rosebuds while ye may
awkwardness experienced on subsequent encounters with someone (despite a smooth first encounter)