My favorite, Top-10, can’t-live-without knitting tools are:
10) Zip-lock bags to contain projects, supplies, yarn...
9) A Pentel Forte 0.5 mm mechanical pencil. I don't normally like mechanical pencils, but I love this particular model.
8) Crochet hook with a microscopic hook on it for beading
7) A cute, small bag for holding travel &/or sock knitting
5) Tapered sewing needle
4) Post-It-Notes for writing notes on as well as using as graph line guides
3) Yarn bowl
2) Interchangeable needles (How did I ever live without these??)
and my number one, all time favorite,
1) Nail clippers. Everyone should keep a pair of nail clippers with the little hook & file thing on them in their knitting bag. Besides the obvious, you can use them to cut yarn, file rough spots on your wooden needles, and in an emergency, you can use the little hooked end thing as a crochet hook or even a cable needle.