Here is how I temporarily attached a Canadian Flag patch to my Tri-star using high strength Neodymium magnets.
Assemble materials: You will need a patch, neodymium magnets, an iron on patch for backing and an iron.
Place magnets on patch observing correct polarity, you can hold them on with glue or use magnets on the other side of the patch.
Iron on the backing, I used a straightening iron because it was handy, but a regular clothes iron works fine.
Make a backing by sandwiching another 2 magnets between the iron on patch material. Attach to your bag and enjoy!