Depends...
It comes down to: your physical shape, your age, your diet, etc. If you work for your body, your body will work for you during multi-day session. I've often played a day plus sessions with little breaks, like literally the 5 minutes you get in MTTs to go to the toilet, wash my
hands and face to wake up, get a snack like a fruit and a glass of water or tea and then I carry on. I smoke cigarettes though, maybe the nicotine helps, but at least I'm a really light smoke and like light expensive ones (won't name it not sure if it's allowed here haha) and one pack lasts me about 5 days or so, maybe 3 if it's a heavy week. I don't drink coffee either, I was an addict drinking over 5 cups a day =D. I guess it also depends on if you're sober or not, how many tables you play, what you do while u play (ye, personally I think it's okay to play 1 table and edit a pic on the side or watch some anime or a game, just pay attention to that 1 table and make sure you're not missing
tells during big hands and taking notes)/ That helps me if I play a long event (like 5 hours LR) and a higher than usual buy in, so I know ill be there for 8 hours and only playing this 1 table to focus. Just make sure u pause/mute whatever it is you're doing when you get dealt a hand you decide to play. Think my longest session was 3 days, maybe 3.5-4 even. Then I probably passed out while at a table still =D (all online btw).