Proper Way to Add Script/Meta to Child Page

I’ve spent hours trying to figure out exactly how Master Pages are supposed to work. I think I have it figured out on simple/small sites. But the sites I build usually involve custom/page specific meta and/or script.

I’ve only found what I would consider “hacks” to add meta to a child section or additional scrips to a child footer section. So far everything I’ve come up with is really messy and time-consuming. Is there a “proper” way to add meta or script that only one child page will use?