Weeklies are the Nexus with Void Burn. Sekiron and the Minotaurs do void damage; stay alive and do some yourself and you'll wreck the shit out of them.
Xur has three great Chestpieces (you already have a good Raspberry though I believe) and Patience & Time.
Ha, Helium is the toughest for me by far. I don't have a good memorable route yet, but I don't usually need them, seemingly? Dunno why. Relic Iron is easy peasy, Spirit Bloom even better. Spinmetal is okay. I much prefer the Divide to the Rocketyard as an area but I think the Rocketyard is actually better in terms of mats, so meh.
The real money for mats is in loops with lots of chests, with the loose nodes as bonuses. I think I've collected like 4 or 5 relic iron nodes on the ground ever, and I have something like 50ish on hand just from getting in "the zone" a couple times and overshooting the number I needed for immediate upgrades.
Just do Archer's Line for Helium. It's super easy. Start out to the left (or right, doesn't matter) then go in all the caves and check the buildings. There's always a chest on top of the big overpass thing that goes from one side of the map to the other.