If you have a dremel type tool and use the cutting discs, super glue the little washer things (red in the below pic) one to the screw head and one to the part. makes putting a disc on easier and you don't lose the washers.
If you have a broken grinder take it apart and get the drive where the disc etc attaches to and you can put it in a drill, handy for getting in to tight areas where the grinder can't.