I don’t believe you can take advantage of functions without a git repo - to my knowledge, they don’t work with drag n drop (that’s really only for very simple, static html + css sites).
You’ll need to trigger a deploy in order for your functions to get parsed, read, and become available for use, and that’s not possible without a repo.
You don’t necessarily need to use continous integration - you could push manually using the CLI, for example, but you will need a deploy.