No adhesive at all. Print on magnetic paper or apply magnet tape to the back of your items.
I use these for my business cards but they can also be cut smaller.
They stick nicely to metal doors and are stronger than most magnet tape.
I buy mine at Office Depot or Office Max.
Darice Magnet Adhesive Backed Business Card 50pc
Some people are like Slinkies.
They aren't really good for anything,
but they still bring a smile to my face when I push them down a flight of stairs.
Friends are Gods way of apologizing to us for our families.
Michaels has a good supply of printable magnetic paper and adhesive magnets.