Make sure that you give an example of setting up a temporary-darkroom plus the ease and cheapness of getting hold of an enlarger and so on.
The metallic and unfading nature of a standard black and white print might be good to mention. Then the viewers will be largely thinking of grey results - so take along some prints on both neutral and warmtone, with different developers, different toners, maybe lith too, all in order to show the variety of results that they can achieve. An explanation of why a safelight is safe(-ish) could tie in to a simplified explanation of multicontrast paper.
Make sure that you name and list some producers of the materials - many people think that Kodachrome was the last film made in the world, after the fanfare of it's ending.
The idea, above, of a pinhole camera is excellent. If you have the possibility, a pinhole neg and a positive from the neg (for example both on plain RC paper) illustrates the neg/pos process very well and is interesting in itself. Make a pinhole camera from foamboard or carton and take it along, with a bit of tracing paper in place of the back.