I added a hole for an 8x3mm disc magnet to Scott64's cool Tyrannosaurus Chip Clip (https://www.thingiverse.com/thing:1274014) so it can attach to a fridge. Even though it's a fairly rigid print it works really well as a chip clip (I use it mostly for bags of salad, actually)!
Just use some CA glue (or similar bonds-metal-to-plastic adhesive) to hold the magnet in place.
Tip: Rough up the side of the magnet that will be touching the glue a bit before gluing. It'll give the glue a stronger grip.
Magnetic_Tyrannasaurus_Chip_Clip.blend | 621.1KB | |
Magnetic_Tyrannasaurus_Chip_Clip.stl | 110.2KB |