- Node.js / Node Ecosystem (Express, NPM, etc.)
- SQL (Postgres is a popular flavor)
- A professional quality code editor such as VS Code
- The basics of deploying an app to a cloud environment such as AWS, Azure, or even just Heroku.
Other skills such as Angular, MongoDB, etc are nice to have and necessary for many jobs, but I think the technologies up above are the “must haves” for a full-stack developer in 2021.
Other runner-ups include jQuery and Bootstrap. While neither are required (and jQuery is basically legacy at this point) they are both common enough that developers should know the basics.