To unlock the Resourceful Agent trophy in The Division 2, you will need to help a friendly NPC at one of the resource gatherings spots which will be indicated by a tin can icon on your HUD.
If you encounter a random group of friendly NPCs picking up supplies whilst you are there, look for the one that has a button prompt to help them. You'll give them some materials, and once they are done with what they are doing, the trophy will unlock.
If you're struggling to locate a gathering spot with NPCs as your roam the map, you can quite often find a group of NPCs that will have a prompt above their head saying they are out gathering supplies when you leave one of your settlements. You can follow them to the resource gathering spot and give them materials when prompted.