I'd focus on the things you want to master. If you like working with pencil and paper, get a spiral-bound sketch pad with some decent tooth (like this, ignore the butthole on the cover) and a small set of decent quality pencils (this one would be perfect).

I probably wouldn't even bother with a blending stump or kneaded eraser. Just practice with those pencils. Learn how to use the appropriate hardness for what you want to achieve. Learn to lighten up or create highlights with that eraser.

I think you'll do better spending your $20 on a smaller number of higher quality tools, and learning to use them well, than with more tools that are going to be frustrating to work with.