I think it's smart to be pro-active and carry a few portable snacks with you. It's good to plan ahead. But if you've forgotten to stock up or are still feeling a little peckish...You could always ask an f/a if there is anything snackish available.
I never mind when a Pax asks for an extra snack. Chances are there is a little extra of something kicking around. We have to dispose of any left overs anyway. I hate to see food thrown out but that's procedure. I'd much rather some of it be eaten rather than wasted.
The caterers are pretty good at calculating what will be used but there is almost always something left. I'd dare to say that there is always something left. That happens all over the world, regardless of where the a/c was catered. So please don't hesitate to ask for a little something if you're feeling hungry after meal service has been completed.
Safe Skies...
f/a