Steps to create a zip file with the changed files of a branch.

zip-git-changed-files.txt

# Zip changed files on a branch checked out from an initial branch.
# Open a terminal on the repository root.
# Tested with Git Bash. Requires 7z installed

# get the last commit on the updated branch 
git merge-base initial_branch_name updated_branch_name

# get the changed files name (with full path)
git diff --name-only COMMIT_ID > diff-filelist.txt

# Create the zip package out of the repository
7z -tzip a ../archive_name.zip @diff-filelist.txt