1: Write down the price of their favorite meals when we go out to eat add it together and then give them that amount of money to go to the store with. Help them plan a home meal and then search for the ingredients, they have to pay with their money. Quickly they realize that with the money we spend on their two out to eat meals we could feed the entire family spaghetti, salad, and some bread. Wow!!! It's fun to watch their eyes pop:)
2: Those packaged sweets they always beg me to get at the grocery I rarely give in to because of nutrition as well as cost. But every once in awhile I say yes. Give them a few dollars and see how much prepackaged sweets they could buy as opposed to making something from scratch...like a cake mix for cupcakes. They will quickly see they could get more for their dollar by making it themselves. Not to mention it won't have all the preservatives etc.
I know there are tons more examples along these lines, but so far these have made an impact on my older girls. It's important that they understand that being frugal is not a terrible thing, just a smart choice:)