I can't remember ever having 3 full meals a day, maybe before I was a teenager... But that's not indicative of calorific intake.
Ditto 8 hours of sleep - not since teenage years, even then it was rare. For the last 30+ years I've probably averaged 5-6 hours sleep per day at best. In fact, 6 hours constitutes a lie-in for me.
In my early 20s I did a bit of a hike - 5 days solo unsupported on Dartmoor. I carried all my food (stuff like granola bars for breakfast/snacks and tins (i.e. of corned beef) for main evening meal. Bedding down in a bivvy bag happened when it was too dark to walk.
I think I still have the map somewhere that I recorded my route on, roughly 170 miles - and I was hardly pressing on. And I was carrying a rucksack (bivvy, sleeping bag, stove, food, couple of tools, some water, etc.) I would've stayed longer and gone further, but for getting back for work.
There's no way I managed to take in my rda of calories
You don't need to maintain food intake for low energy activities like walking, it might get a little uncomfortable after a day or two if you eat nothing but it won't kill you - it'd probably make 90+% of the western population more healthy actually.
Hydration is the main thing.
Dehydration can kill in a few days.
Absolute starvation can take weeks to kill you, and if you have sporadic food every few days you can survive months or even years - sure, you won't be running around much without some serious conditioning but it's pretty much what we're built to cope with.