You don't need #pragma once if you don't include .h files in other .h files, or if you only have a single .h file that includes other .h files. This may sound unrealistic but there are real projects that work that way. You probably do need #include.

I'd say that it's bad to put #pragma once in your minimal set, since it's nonstandard. Why not use plain old include guards?

For me, container_of() is also indispensable. Although maybe it's on the level of 'errno' as being "not really a dirty macro".

I know - I was just spitballing the minimum number, since guards require conditionals too. Though, portability aside, you have to agree that it's simply nicer, since it plainly states the intent without requiring a little dance each time.