LED Throwies are so last year. All the cool kids want Bagel Throwies!
To make one you will need an old laptop hard drive and a stale bagel you're about to put in the bin. Dismantle the hard drive to get out its wicked-strong neodymium magnet (it's what makes the drive head move back and fore and is wicked-strong). Then push it into the bagel, about 3mm under the surface. If it doesn't hold, tear bits off until it does... and then put it on your freezer, next to some Lemony Snicket magnets.
Feel free to lord it over the Graffiti Research Lab with your bread-based magnetic tagging system. OH YES!