How to move Ubuntu into RAM AFTER booting, whilst deleting as much as possible?

This post suggests how to move Ubuntu into RAM

http://dreamlayers.blogspot.com/2012/10/running-linux-from-ram.html

I'm wanting to do pretty much the same, but on a low memory system 512MB or less.

So, given a "standard" Ubuntu 16.04 server, what directories could I delete to trim it down to the minimum before moving the whole thing into RAM and running from there? Put another way, what is not essential?

By "minimum" I mean basically the ability to run many of the command command line utils plus run scripts, interpreters i.e. Python.

The ultimate idea is to be able to reformat the hard disk that the server booted from, and then after that still have most of the "common" command line tools available for carrying out the various tasks required to install a new operating system onto the top of the existing hard disk.

My specific question being, what can I delete from a base install of Ubuntu server 16.04 whilst still having a functional OS for common uses?