Most all-u-can-eat sushi restaurants have a disclaimer on the menu that says you will be charged extra for "wasted food". Which means if your eyes are bigger than your belly, and you leave food behind, you will pay extra.
Steve and I have a particular sushi restaurant that we like to go to when we are in the mood for all-u-can-eat. As far as all-u-can-eat goes, the menu is quite large, and quite good. We've been going there for years and on occassion we have ordered too much food - yet we've never had to pay extra. But that is because we have a few sushi tricks up our sleeves.
When we first start to realize that we are getting full and there is still food on the table, the first thing we do is start bargaining with each other:
"I can eat two more pieces of california roll and the spicy tofu if you can eat two gyoza and the sunomono."
"No, I can only eat one gyoza and the sunomono - you're going to have to buck up and eat the other gyoza."
If the bargaining fails, we pull out the crafty dinner table tricks of a five year old - we put the food on our plate and then take it apart, mash it up, and then smear it around the plate and other plates on the table.
And if all else fails, we have been known to wrap up a few peices of tuna sushi, california or dynamite rolls, chicken wings etc. into napkins and stuff them into our pockets for later disposal - although this very rarely happens anymore as we have gotten much better at estimating our appetite before ordering.
And to be clear, it's not stealing since we've already paid for it - we just don't want to pay for it twice.