I know that it has been established that money doesn’t float. However, what is the buoyancy of the chute packs? In other words, could a chute pack filled with money float? And if so, for how long?
An unopened parachute is going to sink reasonably fast according to 377. On the other hand, one that has been opened and in some manner re-packed could have air pockets which would help it float, but not forever.
A packed parachute would be buoyant and float for a little while, until it gets soaked with water. A factor would be how tightly the canopy fits in the container, i.e. how much air is trapped in the canopy. Bailout rigs are generally a bit loose, as they want to be flexible, comfortable for the wearer. If Cooper hits water with a packed rig, buoyancy is the least of his concerns, as he's dead. However, depending on the current, that would affect how far he drifts downriver before he sinks. If Cooper lands in the water under an open canopy... If there are no winds and the canopy comes down on top of him and he gets entangled in it, that's a problem and he likely drowns. If there's a slight breeze and the canopy lands beside him, that's his best scenario. If there are more winds and he's being drug across the water, that too is problematic. On that bailout rig, the canopy does not detach from the harness without tools. If there is a strong current, once the canopy settles into the water, he's again being drug, as in tension on the harness. Getting out of the harness in those situations would be difficult, compounded by whatever he has tied to himself. The bailout rig does not have the D-rings to properly attach the reserve. I can't see Cooper tying the reserve on with parachute lines and expecting that to be functional. Yes, it's a dummy and would not work anyway, but does he know that? So if he has the dummy reserve tied to himself, it's likely that he has repurposed the container to hold money, which is what the original question was about. There would be air in there, which would make it a bit buoyant, but that wouldn't last very long. Those containers are flaps that wrap around whatever's in there. They are not water/air tight seals, so whatever air is in there would likely bubble out of the corners fairly quickly. The question then is how buoyant the money might be vs. how quickly it soaks.
I know that was more than what was asked. The short answer is that the reserve container packed with money, there would be some buoyancy, but it wouldn't last long at all.