hex key + magnets 

Although I love a good tool pouch, I’ve found the handiest place to keep hex keys is attached with magnets to the seat tube junction. This is a technique borrowed from Grant/Rivendell and it has stuck with me, pun intended. 

If you want to give it a whirl, I suggest a steel bicycle and 3 strong neodymium magnets per tool. I’ve never ever lost one even over rocky terrain, but similar success is not guaranteed. Here’s some blue 4mm MUSA hex keys that I like for their small size and fun color. 3 magnets included with each tool. They are tiny and strong- keep out of reach of children and pets.

Size: 2-7/8” x 1”