Ask yourself: "Can I drill two holes in it?"
If the answer is "yes" then you can make a button out of it!
Step 1: D. I. Y. (Drill It Yourself)
Buying buttons in a store can be very expensive, especially when you need a lot. Here's a very easy way to make buttons from found materials.
Take something flat and small enough to make a button out of. Like this Dominotile!
Then simply drill two holes in it and you're finished!
Needless to say that you should use the right drill for the right material. A wooddrill for wood and a metalrill for metal.
I've tried making buttons out of coins... didn't have the right drill.
Step 2: Make the Buttonhole Wide Enough!
If you're gonna use a rectangular button like this one, do yourself a favour: make it big enough!
The hole should be a little wider then the long side of the button.