Local management of feature branches not yet in upstream master

I have been wondering for some time now, if using Git and making extensive use of feature branches, what’s the most reasonable way to locally incorporate several of the pending changes as long as they haven’t been included into upstream master, and continue to work on other stuff.
E.g. I make several unrelated fixes to the build system in order to be able to continue working and writing new functionality. As long as the pull requests aren’t merged into master, I still need them in some local branch, which should not be master I suppose, since that would create spurious merges each time I actually merge from upstream master afterwars (when the changes are included there).
OTOH, my new commits would then be based on all those commits as parents, and this will become invalid as soon as e.g. one of the pull requests is rejected. How do you experienced developers go about this, please enlighten me! :bulb:

[I had to wait four hours to be able to post this, not that I don’t have other things to do but this is becoming kind of frustrating, maybe those new user restrictions should be relaxed a little…?]

Actually I have not yet tried to simply merge them into master and see how this works out. after all it’s the same commits which I merge locally and which will be merged upstream, so maybe git being the ingenious tool it is will be able to nicely resolve this after all… Still I’d be interested in any best practices regarding this.