Nathan got some duplicate toys for his birthday, so I took him to Walmart to return them. He ended up with over $50 in credit as well as $50 that he had saved from birthday money and allowance. (If I had guessed the toys would have been quite that much, I probably would have encouraged him to leave the cash at home.)
One of the things he has been wanting was a $200 Millennium Falcon LEGO set. I told him that if we went home and saved his money, then he would be halfway to getting it. He thought about it for awhile and then decided he wanted to go ahead.
We spent awhile looking at the toys and he picked out what he wanted. I kept a running total in my head and warned him when he started to approach his limit. Then it was quite interesting. Every time he wanted to add a new toy to the cart, I told him we had to put another toy back (or sometimes two or three).
He saw a large Minecraft LEGO set which was $89. I told him we'd have to put all the toys we had back to get that one and he thought about it for a few minutes and then decided to put the Minecraft set back on the shelf. He wanted a Skylander set which was $30 and asked for my help to figure out which toys to put back (a DVD and an action figure).
I was really proud of him. There wasn't any whining or demands to get more. He didn't try to persuade me to buy some of the toys for him. He asked for help with the math, but he was the one who figured out what he was going to get and what he wasn't.
He was pretty proud of himself, too, walking out of the store with two bags of stuff he bought himself. I know it's early on to be making him responsible for his own money, but I think it's important to give him practice. Hopefully it'll help keep him from making some of the usual mistakes most of us go through when we start getting a regular paycheque.