Before I answer the question, let me make a suggestion regarding your dremmel. First, toss most of those attachments in a box. You'll never use them - at least not for our type of work.
Second, you're using the wrong type of wheel. If you're using the thin red ones, double them up and the won't shatter as easily. You're are better off, however, using the black "mesh" type cut-off wheels. They are (slightly) flexable. The only time I break those is when I'm not carefull putting the tool away. They will break in half if I catch them on something getting it out or putting it away.
Now... Most usless tool. Let me see....
Snake pick (for Adams Rite locks). I does work ***under _perfect_ conditions***, I've never gotten it to work in the real world.
Shim holders get an honorable mention.