Intended for light artillery units, this would have been used to replace the haversack and blanket roll. These would not be carried on the back, but rather by a handle, which is no longer present in this example. 
The bag is in used condition with a few small holes and most of the leather is cracked or broken. 

On the back side, there are different markings, the most prominent one being a unit marking of the New Jersey, A company, field artillery. The other markings appear to be a name and a set of numbers. 
On the inside, we can see it was made by Rock Island Arsenal in 1910.

These packs are rare and don't come up often for sale so this would make for a perfect item in your collection that will set you apart from others. 
 
Only one available.