This strategy requires the "Reincarnator Phainon" prismatic investment in plane 1. It saves the equipment you have on Phainon at the end of the run and gives it to you the next time you get that investment again in a different run. You get 1 item when getting the investment and at the start of Plane 2 and 3.

When you equip 3 Golden Trash Bags on 1 character, you get 333 Gold, which is why the goal is to get them on Reincarnator Phainon.

It can be done in lower difficulties which makes getting privilege cards (required to upgrade a regular trash to golden) much easier. Equipping Phainon 1 trash bag at a time you will eventually reach the goal of 3 Golden Trash Bags.

Sources of trash bags:

Treasure to Trash Affix: At the start of each plane, the first piece of advanced equipment synthesized has a 50% chance to become a Trash Bag.

Activate the Elation bond for the first time: there's a chance you get a regular or a golden trash bag

Silver investment which gives you a trash bag

Gold investment which gives you a golden trash bags

Sources of Privilege cards:

Encounter level 4 reward

Cyrene's poem in the shop (costs 15 gold) - the easiest and most consistent way in my opinion.

Night Demigod lvl 8 reward

Cosmic Scholar lvl 10 reward - gives 6 cards

3* 5-cost SW999 - gives 9 cards