Why is there a need for a package manager inside a container at all? Aren't they supposed to be minimal?

Build your container/vm image elsewhere and deploy updates as entirely new images or snapshots or whatever you want.

Personally I prefer buildroot and consider VM as another target for embedded o/s images.

So if i have a docker container which needs a handful of packages, you would handle it how?

I'm handling it by using a slim debian or ubuntu, then using apt to install these packages with necessary dependencies.

For everything easy, like one basic binary, I use the most minimal image but as soon as it gets just a little bit annoying to set it up and keep it maintained, i start using apt and a nightly build of the image.