Mercury is the only metal that is liquid at room temperature. This would seem to make it ideal for a chemistry experiment but its slow-acting toxicity is a cause for concern. The metal itself is not toxic because it doesn't easily pass through the skin (it is if eaten etc though), but it does release fumes which can poison one - and also many of its salts, such as mercury(I) chloride, are very toxic and can be absorbed through skin and even latex gloves!
In fact, there was a teacher who did an experiment awhile back with mercury(I) chloride, which made it through her gloves, and through her hand - about 7 months later she was dead.
One thing you may be able to do is bring a mercury thermometer with you and explain that the liquid inside is mercury metal, then get a good heat source set up and a penny - which is zinc. Heat the penny above ~420C to melt it, and show people by moving it around with your pencil that the zinc has now been liquified. Do a comparison between that and the mercury in your thermometer.
Make sure to put the penny on a piece of scrap metal though because it likes to bind to its surface as it resolidifies!
