My personal essentials are:
217 - blending and basic application.
219 - great for smudging liner and applying shadow to lower lash line.
224 - imo, better blender than 222 and more versatile, also good for application.
227 - my "magic eraser", great for blending, also good for basic application.
239 - dense application of color.
242 and/or 252 - dense application of color also handy for applying paint or concealer.
Hope this helps!