Tao is the type that enjoys finishing eating as much as she does the actual eating. After she's finished though, she'll forget that she had already eaten and want to eat some more. So she probably could eat this much, but it's not a habit of her's to do so.
Pay? Ragna? If he could pay for his food he would probably be healthier, not that he's not fit but you get my point. Though he does seem to have bad luck with women. They either want to kill him, arrest him, torture him, or in this case make his bounty bigger by dine-n-dashing.