Most painless way to set an editing checkpoint?

[Sean McAfee]

Sometimes I want to embark on a series of editing operations that I'm
not sure I'll end up keeping.  None of the various ways I've used to
revert to a previous state are entirely satisfactory:

1.  Just undo everything.  It can be difficult to know when to stop,
especially when the changes are scattered throughout the file.

2.  Save the current buffer contents in a temporary file.  But then you
have to remember to delete it afterwards, as well as apply some
buffer-association boilerplate in the meantime.

3.  Stuff the entire buffer contents into a register.  This solution
probably has the least overhead, but I worry that I'll accidentally
overwrite it.  I can use a register I don't otherwise use very often,
but then a small but annoying fraction of my attention is occupied
remembering which register it is.  This solution also becomes less
feasible the more files I want to simultaneously apply this treatment
to.

Any other suggestions?