I was asked recently what the tools of the trade were for a computer repair technician. Here is what I think they are from my years of experience.
Lots of CD's / DVD's. You need to have all kinds of software in your toolkit. For instance, Windows XP, has more than one disk in fact there are tons of variations. Do you have Home or Professional? Are you using a retail version or an OEM version? What OEM version do you have, is it Dell or HP or Lenovo? Plus all the other tools you need like virus programs, disk utilities, memory checkers, etc. I carry a 64 pack of CD / DVD's, and still find myself sometimes wishing I had bought more stuff.
A Laptop with a mobile internet connection. Many times you're out in the field, and you need to look up a service manual, or get the drivers for one thing or another, and it really can be a huge help if you're able to get online no matter where you 're at. Also when it comes to that, you probably need a pretty big battery as well. I usually have two 12 cell batteries charged up and with me, so that even in an emergency I still have up to 12 hours of battery life that I can use my computer. Nothing worse than running out of batteries, when you're running a virus scan on a hard drive that you've pulled out a client's computer.
You're also going to need a good set of computer tools, that are equipped specifically with precision screwdrivers. You'll use these quite a bit while working with laptops. Plus of course the needlenose pliers come in handy more often than you think.
Also there are numerous miscellaneous tools you'll need like an external USB connector for hard drives that will allow you to attach IDE and SATA hard drives directly to the USB port of another computer. Multimeters that let you check the function of electronics in your computers. Anti-static wrist straps to protect you and your clients system while you're working on them.
Honestly it takes a period of time for each technican to get a feel for what they feel will be essential to their computer repair endeavors. Hopefully this will give you a legup in putting your very own toolkit together.