Strong "you can't let good food go to waste" in the post-war generation, including in my own family. It's so ingrained even in the next generations that many of us will just "finish their plate" even though there's no necessity there. Some of us are quite well off now, but attitudes around food haven't changed. You have to finish your plate. You can't let good food go to waste. People elsewhere are starving. People worked hard so you could have this food. You don't know when you'll be able to have a nice meal like this again.
Like you, I realized the difference when I met people from different, well off, culturally food-secure backgrounds. They'd just stop eating, and throw the uneaten leftovers in the trash. Doesn't matter how good the food was. Doesn't matter how expensive the food was. Doesn't matter that you could eat the leftovers later.
I had a really hard time landing on some reasonable middle ground (you can save leftovers, but you're allowed to stop eating when you're full, etc.). Made me realize that it's so much more cultural than personal. Also raises questions about what we're going to pass down to the next generations, intentionally or not.
These are basically small concrete boxes sunk into the ground. They're only meant to stick out a bushfire for a few hours.
You could probably just keep a few bottles of oxygen or a carbon dioxide scrubber stashed in there, just in case. If you can spend $10,000 on one of these bunkers, spending a few hundred more isn't going to make a difference.
Anything longer than a few hours would get dicey anyway without room to move around, without room to stash water or food, without a toilet or beds.