That's a great idea Jaycee. Most kids love fruit and are happy to snack on it, and once they get used to the idea of grabbing a banana rather than a bag of potato chips when they're hungry, that's what they'll do automatically.
Veggies are also a good healthy snack, so why not stock up on red peppers and carrots next time you shop. Cut them into batons and they'll keep in an airtight box in the fridge for a couple of days - easy.