All of mine have the same tools on them. My kids like to steal them and hide them from me. I thought I was losing them, so I would buy more all the time. When I moved shops, I ended up with a nice pile of "found" drives.
When I have multiple machines in the shop, it makes it more convenient to be able to grab one and go to work. I have one on my keychain for those random repairs when I'm out and about.
I carry two. One 4 gig and one 8. One is multiboot and the other just has a large mobile kit on it. If I need more than computer comes back with me. I have 7 more at my shop.