Looking for the best hauls with a wide variety of stuff, Corvega seems to be well stocked but difficult to navigate

I got a lot of my core materials just scrapping houses, furniture, rugs, toilets, tires, etc, in Sanctuary. Hospitals will have higher grade components contained in things like Microscopes, Office buildings and factories will have lots of fans, typewriters, circuit boards, etc. The one that really took me by surprise though was Jamaica Plain, in the south central region. It's pretty easy to clear of enemies if you just get on top of a vehicle in front of the Town Hall, and the hallway to the treasure room yields TONs of infinitely respawning loot if you just disarm the turret lasers. Don't forget too that high tech robots also have good loot items.

I have played far enough to be almost level 40, and I haven't bought anything and have only done two minor weapon mods. There is LOTs of scavenging in the game, and it's not hard to do it if you have high Strength and Strong Back stats. I haven't even used companions since about level 10 either, because Lone Wanderer yields more carry weight and less damage when solo. You can carry up to 450 weight solo with the right perks, and the last two of Strong Back let you even run for short periods and fast travel when you're over your weight limit.

A quick way to level up early on is by playing through all of the Scribe Haylen and Knight Rhys side quests when you get to Cambridge Police station.

Basically any of the large complexes are the best, a good example being Corvega. They all respawn, so you can go through them every couple of game days. Of course, the baddies respawn as well.

Fort Hagen

Super Duper Mart

Saugus Ironworks

Vault 114

Vault 95

Parsons Mental Hospital

BADFTL is good. Have your lock picking skills up or bring Cait. Not a big place but very good. Walking distance from Bunker Hill.

Federal Ration place near Sunshine Co op also. Lots of everything.

Wilson Atomatoys Corporate HQ (good number of giddyup buttercups that break down into screws)

Corvega (large number of coolant caps at the lower floor with the assembly lines that break down into aluminium)

Wattz Consumer Electronics (good number of junk items that break down into copper)