I have about twice as many as listed below, because it's nice to be able to setup completely different workspaces and occasionally get the "quick fix" of a preprocessor via VS Code as opposed to Gulp, etc. (especially if a colleague is unfamiliar with one or the other.)

Also a fan of dark themes, as well as VS Code Icons. But I haven't listed any UI or icon themes below.

ASCII Decorator

Beautify

Code Runner

EJS Language Support

ESLint

GitLens

Go (Rich Language Support)

Gulp Tasks

JSHint

Live Sass Compiler

Live Server

Project Manager

Run On Save

Settings Sync

Shell Launcher

Todo Tree

Vetur

VS Live Share

Vue

If I were to pick a Top 5 "Most Used" out of the list above:

Settings Sync

Live Server

Project Manager

GitLens

Shell Launcher

The Shell Launcher is great for cross-platform work, btw. So you can default Git Bash for Windows, switch to Powershell when needed, and when the project is loaded on another OS, it'll use the native bash. All within the VS Code terminal. These are basically what are always used for any project done within the VS Code IDE.