Picking up a theme that arose in another thread, I'm starting it afresh here. My question is, what small items that can easily be carried in pocket, wallet, briefcase, etc., will also do double duty if necessary?

These items will probably pass security checkpoints because of their obvious uses.

For instance, hand cleaner usually contains alcohol and can therefore also be used as a fire accelerant. In another instance, dental floss can also be used as sewing thread or even fishing line.

Feel free to chime in.