I use a sharpie and mark them as used, then I use them to cut my cardboard, It makes quick work of it, and with a bad shoulder I have trouble tearing it into pieces. This way I can cut it up and stack it.
As far as tossing them, just use one of your old containers. There's no need to dispose of them like sharps at a doctors office! They aren't contaminated with body fluids or disease! Just put them in something and toss them.