Some time ago while browsing at a thrift store I was lucky enough to find a "Stitcher's Mate" storage box. While it is intended mainly for sewers, it works perfectly for my crochet gear! It measures about 9 inches by 3 inches and stands about 2 1/2 inches tall. It holds plenty of stuff and yet is not too bulky for me to carry around in my project bag.
It is divided into 2 sections, the top section is shallow and magnetized. I carry yarn threaders (I can't live without these!), yarn needles, safety pins, pins and sewing needles.
The bottom section is deep and holds my "Knit-Chek" gauge checker/hook size gauge, pens, pencils, sticky notes, hooks, eraser, row counter, scissors, yarn cutter, tape measure, calculator, and crochet stitch markers. Can't forget the nail file for those pesky nail tears that snag the yarn, and lip balm!
So what do you carry in your crochet kit that you can't do without?