Honestly, I would just read through all of it including the Appendix. It really does over the essentials of the Rust programming language, with everything there being an essential piece of understanding and using Rust.

The harder thing is choosing what to read after the Rust Book. Rust’s standard library constrains itself to only core functionality, so functionality like regexs and serialization are implemented in separate crates. The https://lib.rs/ and https://docs.rs/ sites are invaluable for expanding your knowledge of the Rust ecosystem. The Cargo.toml file for a given project will point you to what crates are used in the project.