What are the most important non-technical parts of an indie hacker's stack?

As a first time indie hacker, I feel pretty overwhelmed with all the tools people are using.

What are some of the most important "buckets" of your non-technical stack, and what are some common providers for each one?

For example, I just finally learned what a CRM is, despite having heard of "Salesforce" and "Hubspot" for years now.