In general I end up switching hooks on any larger projects, because I simply cannot keep hold of one hook for that long. I am always misplacing hooks, in another project, in between the couch cushions, or stolen by a two year old. To remedy this problem I probably own at least 6 to 8 each of my most favorite sizes to use, all made my Boye, my preferred style for hooks. In fact, I have almost entirely eliminated the Susan Bates in-line style hooks from my collection because I find the more open throat of the Boyes easier to use.
Imagine my surprise when I realized that I had started making my Reversible Rowan Tree Vest with not only a Susan Bates in-line style hook, but a hard to find "Quick Silver" size "C". I did not mind the in-line style when working with DK weight Madelinetosh in a tight stitch to better hide the many color changes. But I wanted to be sure to have a backup, in case I misplaced the one and only hook I had. I hunted through every big box store and the nearest LYSs in vain, and had many scares when I thought I had dropped it, and actually DID drop it once, at the zoo. I found it every time, and managed to hold on to that one tiny hook until I completed the project, but I highly recommend making sure you have at least one backup hook, just in case.
By the way, if you are ever looking for a back up "Quick Silver" Susan Bates hook for yourself, I did finally (after my vest was complete) find a few available on Ebay. I have also now found the one Portland area LYS which carries them and had to pick up a couple, just on principle. If you are in the PDX area, try Twisted on Broadway!
How many hooks do you keep around of each size? And are they mostly Boye or Bates?