Not sure about food, since the food will have already been priced......but !
Flights is different. This dude pays the same as the guy next to him. Yet the guy next to him will get an extra charge if his luggage is 1kg over the allowance.
Since extra weight = extra fuel costs etc right ? So if that's the case why does the dude who weighs 3x the guy next to him pay the same for tickets..