Core knowledge starter pack?

I've been reading some SaaS start-up ideas and noticing some themes. Like some background integrating OAuth. Knowledge of the Shopify or Stripe API to integrate some sales.

Wondering if maybe some could share what knowledge they would consider core when starting a new Indie "thing". Granted not all these "things" are measured the same. An info-product might be nothing more than an ability to write, convert Markdown to PDF/Mobi/etc, and a site to collect subscriptions. So qualifying the core knowledge with product scope/type might be useful. While a tool to monitor build a community might have a large set of "core" requisites. I suppose this might be too open-ended, but thought I would ask.

I'm wondering what do people think the core knowledge starter pack is for various indie projects they see here on IndieHackers?