Craft Magnets

Even better than the small magnets that can fall off and create a choking habit are those magnetic business cards lots of business cards hand out. They can be cut out in any shape with a sissor and will pick up paper clips and other small items. I get them from my work place whenever we have a location that change addresses. Most printing places make them, so you could probably buy a whole box of 'blanks' from them for a small amount of money. I also use them to glue pictures to for easy display on the fridge. Grandparents love getting the school pics already mounted for display.

I say go bigger rather than smaller...

If it were me, I would get the largest magnet that will work for what you're doing. Even if the 1/2 in will work, as long as 3/4 inch isn't too big for the craft, it could come in handy. The extra quarter inch of diameter can mean a lot more stick-to-it-ness in a future project where you might want to attach something a bit heavier..