1: When you reach the first jet of flammable gas, look above the rafters and you will see the sack above. Many of these are hard to see in the dark, so be sure to use your Survival Instinct to spot them.
2: In the center of the large main room, on the south side of the center wall, look up to find the sack hanging.
3: When you reach the corridor with the cells along the side to the northeast, there will be a sack towards the end up high.
4: When you reach the gate that you need to hop over, there will be a sack directly ahead of you that you can see while on the top of it.
5: Once you pass over the gate, look back down to the door you climbed over and there will be a sack hanging there.
6: When you reach the path that leads west at the very far north, there will be some fences and enemies. When you first reach the area, look up to the right and the sack with be there.