Dreamweaver Locations
There are some one-time items to get, and some recurring boxes.
(spoilers throughout)
Dreamweaver One-Time Items

The recurring boxes might show up, they might not, and only a couple times per day. And when they do, there are a few locations they might show up, so you have to check all of them. I'm positive that I have not found every single location, but I've been trying to grab screenshots when I do.
Dreamweaver Recurring Loot Boxes

Of the items that might be in a box:
- common raw items: cog, pipe, spring, screw, lens, glass vial, magnet, plasma globe
- common crafted items: gyrostabiliser, accelerating apparatus, compass, animus servo
- uncommon crafted items: clockwork furnace, vapor condenser, aether boiler, super charger
I've never seen them give:
- solvent, tin can, cloth, horn, ice flower, snow cone, snow globe, dynamite, reticulated spline, gearbox, radio beacon, telescope, telephone, chromic acid, poison detector
Easter Eggs
other hidden things that can be found
Coded Message in Evergreen Meadows (using dreamweaver)
Rainbow Alpaca Hat in Evergreen Meadows (using Shearing Crook), but can only be reached by swimming, and that takes the Diving Suit and Helmet you can only get by reaching L7 without a profession. Watch for possible updates in future game releases.
See the previous scavenger hunts note for 4 other outfits
Gear Sword is essentially a scavenger hunt, too, since it requires a raid party to get a key from the boss guarding the treasure chest with the crafting plans, and then time (searching boxes and fighting enemy groups) to get the crafting materials. Unfortunately, right now the reward in the Fogstone Depths and the Fogstone Cavern is the same.
Boxes and Barrels
One of the December 2021 updates was the addition of boxes and barrels that might have free loot in them.
Locations to check the boxes and barrels
Not in all map locations yet, and the locations with common items (ex: No Man's Landing) might give items multiple times per day, but in the locations with rare items (ex: Northern Slurries) you might have to check all the barrels and still only get 1-2 items per day. Blue text for the rarer materials.