The Long Walk Back To The Toolbox
Some of us use tools in our everyday jobs. Often, it's the same tool all the time, like a screwdriver, cutter, wrench or allen key.
You might find that you need that tool, and didn't bring it with you when you first approached your task. So, back to the truck / car / toolbox you go. Wasted time.
There is one thing we all carry in our pockets - the car keys. A keychain is a good place to keep a spare tool. I have a 7/16" wrench on mine, since all the bolts on my equipment use that size nut. Many times I've been up on a tower, needed a wrench that I did not bring up with me, and out come the car keys. Saved my bacon many times!
There are many tools available from many sources. A walk through Lowes or Home Depot's tool departments will show that all the manufacturers make mini versions of their tools.
You can also keep a Leatherman style tool in your pocket. There are a few models to choose from, some with Needle Nose pliers, some with scissors and so on.
I'd suggest you buy a good quality mini tool. Being small, you're going to put a lot more torque on them to get the job done, and cheap steel will just bend and you'll be tossing that tool pretty quick.