Sure, maybe "stashed contributions" is simplistic to the point of being wrong. It isn't that I'd like a better mattress to stuff paper under.

In my mind, money is an acceptable enough fiction that I can convince someone to allocate me a hamburger for lunch today. The fictional aspect of it is very handy in performing the time-travel of paying my future self part of my wages of today.

Times change and in the future a hamburger may require more or less money as it did today. My bet is that in the long run, that hamburger will be mostly the same or a functional equivalent will cost less because human ingenuity is an unlimited resource.