I have an OLD canvas bag measuring 14 x 11", opens to two pouches. It has a leather strap on the back that makes it look like it was possibly used as a backpack.
Printed on the front is "2 SEP.CO. 16".
Inside is stamped "Ridabock & Co., 141 Grand St., New York". There is a second stamp, most of which is too faded for me to read, but I can make out "Sep 1896".
I have researched this company and see that it was at that address (141 Grand) in the 1890s. (photo of an ad I found is included, which also states that the company are "Manufacturers of Military goods of every description, U.S. Army Officers Regulation Equipments a specialty", from march 1894 Army & Navy Journal). The last mention I can find of Ridabock at that address is 1896.
I find references to "Sep. Co." as Army "Separate Company", but I can't really find anything in particular beyond that to explain who might have used this.