Ruined buildings are packed with things worth taking, but carrying them home is another matter. Supplies run low, infected wander into places that seemed quiet, and bad weather has a habit of arriving at the worst possible moment. The full version is already unlocked, so the whole experience is available from the start, either solo or with friends.
There is a nice bit of tension in how ordinary scavenging can go wrong. A quick trip for food or gear can turn into a long detour through a street you had no intention of visiting. That scrappy, unpredictable side of survival gives the wasteland some character.