stash is a useful command to save your current work files, including new ones (i.e., untracked).
# push a new stash including new files at the top of the stack with name "WIP"
git stash push --include-untracked -m "WIP"
# check that there are no left unstaged, untracked, and staged files
git status --short
# see that new stash entry is at the top of the list
git stash list -n 3