Any feature to add code snippets in headers/footer/anywhere?

I would like to add code snippets to all headers/footers across my site. I know you can add CSS with the customize option, but I don't feel comfortable adding code snippets there and I'm not sure if javascript works there.

I'm trying to add stuff like favicons/google analytics into the header. I know it can be done with other plugins, but would prefer not to install more plugins.