Except for expedition rewards, new resources can (and should) be created in the settlement using new workbenches. These benches are set up in build mode, just like at the old base. In order for a similar button to appear in the settlement, you must first complete more tasks of the second act. Build mode is unlocked during one of those missions. In addition to workbenches, you’ll be able to set up a variety of storages. There is never enough room for new resources!