How to commit some files to the master branch and some to a separate branch?

Question

git

There are two brunches. b0 b1
b0 = master - contains common files
b1 = custom - contains special files for b1
There are thousands of files and directories on b1, some of them are common, some are special
How to add files on b1 that are intended only for b0 and run them and then also for b1 branches?
That is, ideally, say git add "use gitignore-for-b0" - commit / push,
and then git add "use gitignore-for-b1" and commit / push.

Answer 1

git stash is for you

Answer 2

Prepare a temporary .gitignore file for the first case, put it in the root, then git add -A .
then we return the original .gitignore to its place, commit, push