Twenty-six cases. One of them is yours.

Pick a case and keep it sealed. Open the others one at a time, and every amount you reveal is an amount you are not holding. Now and then the phone rings, and the Banker offers to buy your case. Deal, or no deal.

How it works

Your case stays shut. Whatever is in it is what you are playing for, and you will not find out until the very end.
Open the rest in rounds. Six, then five, then four… You want the small amounts to come off and the big ones to stay.
The Banker calls after every round. The house lowballs early and pays up late, exactly as it does on television — or hand the phone to a friend and let them talk you out of it.
Two cases left. Yours, and one other. Keep it, or swap.