First, we should probably do the simplest thing that works right now, which is probably just making items disappear over time.
Once that’s in, it would be interesting to start having the disappearances make sense, and have them either go sonewhere or be expended instead of merely evaporating.
Probably the next step would be to evaluate a danger level for different areas, and have scavenging from less dangerous areas happen faster.
After that we could either try to factor in value of scavenged items in some absolute sense, or if factions exist we could have them try to enumerate and satisfy their needs for scavenged items.
If we get that last part in, it leads to them actually accumulating the scavenged goods at settlements or consuming them.