I don’t have very many mutators atm, but I’d say either bandit or the one that increases ranged damage as you pickup ammo

For my long gun Im using the bonesaw with overflow and bandit mut. And I’ve been switching the sidearm around depending on the situation but I’ve found that enigma works well in many many situations with many different mutators. I’m still not done with my first run through though, so I’m still on the lookout for a new favorite lol

The best thing I’ve found so far is just to run adventures. Once you get a few levels into the archs and start getting a build going you don’t need to upgrade as much allowing you to start saving more. I was able to come out of one up 5000 from when I went in. Ofc results may vary depending on where you are and it may take a surprising amount of time if your build is lacking. I personally have not found any trinkets that increase the amount of scrap you collect but there were a few of those in R1 so it might be worth it to look out for those as well. Another thing: don’t worry about collecting things you already own. Often times when you pick up a ring or something which you already have, it gets converted into scrap.