David Gerrold’s 1973 The Man Who Folded Himself is a standalone time-travel story.
Assured by his Uncle Jim that he will inherit a vast estate, Daniel Eakins is unpleasantly surprised to discover (after his uncle’s demise) that his legacy is not the hundred-million-plus dollars Daniel had expected. What he gets: the far smaller sum of six thousand dollars … and a belt.
It is a particularly fine belt. In fact, closer examination reveals that it is a fully functional time machine.