This right here is a super cool & rare Schwinn approved (made by Carradice) saddle bag, large & in charge. Significant storage space right behind your butt. Perfect for your vintage 70's randonneur project.
Fair warning, due to the age of this item the straps are somewhat fragile. I would recommend acquiring some leather seal and rubbing that into the straps, & leaving them for a day or two. This should keep them in good condition & resist water.
Check out our other great listings of used/NOS cycling parts and accessories, you may find something you want/need!