Our family gets pretty creative: There have been piggy banks filled with loose change (guess how much $money is in the bank), pencil boxes filled with random school supplies (guess how many hours kids go to school each year) and even a package of Oreos (If Oreo cookies were laid side by side, how many would it take to cross the Golden Gate Bridge? Answer: 28,800)
But most of our "jars" are containers filled with candy, something like this:
And of course, glitter makes everything cuter, so the edges are dusted with a little bling :)
Update 5/28/13: Apparently I didn't finish my thought when I originally posted this! Each jar gets a number so that people can start anywhere on the table with their guesses (for instance, you could pick up jar/container #8 and write down the number and your guess, then move to jar #12, etc, until you had made a guess for each jar). Once everyone has made their guess, the M.C. reveals the correct answers and the person who guesses closest wins that jar/container!
This is a fun game for a crowd because there can be MANY winners :) You may choose to only allow a person to win ONE time. However, if they were the closest guesser on a future jar, they could choose to exchange it for their first jar, giving the original jar to the next closest guesser.
To see how we modified it for a bridal shower, see this post.