The amount of gold one gets from gold bags in NG is so low ($19-$100) it's not even worth the effort to pick them up. So the main source of "income" if you will comes from keys.
Here is a list of places (or occasions) where one can get a key 100% of the time in each NG:
- RB1. Small key from the chest after killing the first enemy (Horned Wilding).
- RB1. Thane V1. Medium key near the chair to the left of Thane. (not obvious at all, thanks to the forum for the tip)
- Any RB. Small key to the right of Archivest (found mid-way through the cut scene prior to the fight).
- Any RB. Medium Key drop after killing "the Beast" in the arena for the 1st time.
- Any RB, Large key from killing MX-Goliath.
- Use Key treasure map, get a key each time you go to top of the Thane tower (look and click to your right). Large key for the first time, and small keys afterwards.
Here are the additional places/occasions where I also have found a key (and the approximate chance)
- In the beginning of any RB. Small key lying on the ground near the lower-left corner of the screen. <10%
- Any RB. Small key from the chest near the castle gate after killing the second enemy. 10-20%.
- Any RB. Small key lying on the ground near the chest to your left before or after killing the second enemy. <10%
- Any RB. Key drop after killing the second enemy near the castle gate. I have gotten small, medium, and even one large key (after killing Fel Siren). Very rare. <5%
- The side entry in the plaza (where the enemy drops down from a hole). One can get a small key from either key drop or the chest. 10-20%
- Any RB. In the Library hallway. Lying on top of the railing to your right. 10%
- Any RB, The chest to the right after entering the open arena. 10%
There may be other random key-drop after a battle, but they are too rare and sporadic for me to remember.