Items that you collect inside a Heist are considered contraband. It’s an indicator to show you which items you’ll lose if you die within the Heist. All items you manage to take with you will lose the Contraband indicator when you leave the Heist.
If you die after the lockdown and lose your contraband, a Heist attempt is only considered a failure.
Party play in Heists, if you die and drop your contraband, your party member can collect it for you and then share it if they’re nice.