I followed the suggestions in the website http://richardsont.people.cofc.edu/safe_solar_folder/ with a +2 diopter close-up filter as my first lens and a mystery -25mm (??) lens as my second one, using a shelving upright as an optics rail.
Pro: You get a nice big 2-3″ image for everyone to look at. It is fun to rearrange as the sun moves in the sky. You can photograph the projection with any kind of camera.
Con: It is kind of fuzzy. If blown up to larger sizes, you get one edge blue and the other red due to chromatic aberration. You can spend more for non-aberration lenses.
Upshot: A great interactive group activity.