Maybe some sort of “military broadcast” or other hints about a military base of some sort? They should know that others may try and clean it out before they get there which introduces a ticking clock element. Maybe the message includes a warning that if the security system doesn’t get disabled the base will self destruct in X many hours?
Then when they show up, they encounter enemies (zombie mob/other survivors) and have to work together to defeat them. When they succeed, they get the things they need (food, weapons, a defendable base)