Mosaic From a 4-H'er
Set a table, build a birdhouse, plant a garden, make a scrap book, make friendship bracelets, any type of food, make a duct tape wallet, make a piece of clothing, blow a bubble with gum, make play dough, make paper beads, write a letter, tie your shoe, make soap, any type of mathmatical method, make a snow globe.
These are just a few demos that I have done or thought about. Make sure when conducting your demonstration to make it fun, catchy, and full of personality. This will make the judges or audience. It can also make it memorable to take first place!
Also, it is important to describe why it is important to know how to do what you are demonstrating or how it can be useful. And also warnings or things to look out for as far as safety goes. This generally comes in the conclusion. Also, if there is something that is inexpensive, than include prices of the supplies.
For example: If you choose for a playdough. You could say that in comes in handy for a craft project while babysitting or it makes a great craft project and take home in vacation bible school. Be sure to not let the children eat the any of the supplies or finished product. Children may need parental supervision.
While it is not always necessary, judges often find it impressive if you list and discuss the nutrition facts in a food talk and point out a positive health benefit.
For example: "Peanut butter is a sweet treat the contains no cholesterol, but has a lot of protein in it."
This shows your judges or audience you have complete knowledge of the subject.