Get a large bag of candy and a big see-through jar or container. You can use a jar filled with jelly beans, Hershey kisses, gumballs, or even funny shaped sweet tarts. Fill the container with as much candy as you possibly can. Make sure you count the number of pieces of candy as you put them in.
As guests arrive ask them to look at the container and write on a slip of paper their name and how many items they think are inside. The guest who comes closest to the actually number wins!
If you place a mix of candy in the jar, not only does it give a nice assortment as a prize, it can also make it much more difficult to guess how many are actually inside the jar. Try mixing miniature candy bars with M&M or red hots and it will really be a challenge!