Traders are the backbone of progression. They turn scavenging into a directed loop with guaranteed rewards and a clear payout.
The quest loop
Take a quest, clear the marked building, return for dukes and a reward bundle. Repeat. It beats random looting on every axis.
What to buy
Spend dukes on things you cannot easily craft: vehicle parts, skill magazines and high-tier weapon mods.
Raising tier
Tier rises with completed quests, and higher tiers stock better inventory. Do every quest available rather than cherry-picking.