Wishing for option to automatically save nb file with the equivalent of an mx file embedded in it

New feature suggestion:

It would be really great if Mathematica offered a way to automatically save an enhanced version of .nb that contains, in effect, the equivalent of a .mx file with the results of all of the cells that have already been evaluated. This combination .nb/.mx file (perhaps to be called .nbx?) would avoid the time/effort required to either: (1) save a .mx file at the end of each Mathematica session and re-load it at the start of the next session, or (2) redo the evaluation of the saved .nb file at the start of each new session.

Thanks,
RM