The school cafeteria is an intricate social jungle, complete with its own class hierarchy and economic system. Within this complicated culture is the time honored tradition of trading lunches, which helps kids improve their given lunch situation while throwing them into a crash course on basic capitalism.
Kids rarely eat their whole lunch. When given a snack that they find less than favorable, they'll try to trade it for something tastier. Every brown paper bag is full of high and low value items that can make or break your kid's chances of improving their meal for themselves.
One of the most common mistakes parents make is to fill their kid's lunch with high-value items, such as candy or desserts. While this tactic is sure to give them a nice sugar rush for the end of the day, they wont feel as much of a need to participate in the trade-game, leaving them out of valuable life lessons that the cafeteria can provide.
In real-world economics, this can lead to a personality disorder known as Paris-Hilton-Syndrome, where the afflicted never works for their advantages in life and develops a false sense of entitlement for the things they have.
Another error is to fill the lunch with only healthy options. While parents assume this ensures their child's nutritional needs will be fulfilled, possession of only low-value items prevents them from entering the trade market all together. A lot of that healthy food will end up being wasted, as most kids would rather spend the afternoon hungry than eat a bag of celery.
The key is to provide them with a full spectrum of deliciousness. Diversify their portfolio with something sweet, salty, fruity, and filling. An expansive menu will appeal to their taste buds as well as those of their lunchtime companions, who may be willing to make a trade if the price is right.