My grandpa taught me how to do this along time ago and I figured because this is the site that is the depository for all how toing knowledge why not add my own weird trick.
Step 1: Locating the Strip
Take American paper currency more than the one (one dollar bills do not contain the magnetic strip) and hold it up to a bright light. I recommend doing this with five because this may make it so that you can't use the bill in a vending machine or at least it will think its a one. I also recommend that you do this with an old bill because it makes extraction easier. When you look through the five you should see a strip of something that has the words USA FIVE written in small black print on it.
Disclaimer: This may be illegal. This is only for informational purposes.