This commercial uses the 1930s standard, "We're In the Money" to advertise the "McDonalds' Money" promotion: Buy a meal at McDonald's and get a token worth 50 cents to spend on your next meal there. That way, people would have to come back again and again, and would always spend more than just the 50 cents.
It was a very clever idea. In fact, Canadian Tire had been doing the same thing with its Canadian Tire Money for about 50 years before this McDonald's promo. And Canadian Tire is STILL doing it today.