I like systems that work like many Skyrim mods (my favorite is Realistic Needs and Diseases) that have "light" or customizable versions. I think that systems that are constantly bugging you about being hungry / thirsty / tired are mostly annoying. As most open world games are usually in the tune of 30-60 minutes of day, and the same amount of time for night. Needing 3 meals a day and 8 hours of sleep...means that the
game is bugging you about something every 5-15 minutes. That's pestering. Slower games (like SCUM...which I looove), can do intricate detail with needs, but the game itself is much, much more slow-paced than many people would prefer (about 4 hours of day and 2 hours of night). You still seem to get hungry a bit too often to be "realistic", but it's not that intrusive because it's so much more spread out in real-time.
Ideally, I like systems that work as follows:
- You need to eat at least once per day. If not, you suffer penalties, but will not "starve to death". The penalties will simply increase until they become problematic and ultimately crippling.
- What you eat will provide you with specific bonuses. Characters will wind up with favorite foods, as they nicely augment their abilities and playstyles. Nothing huge. Just a noticeable edge.
- Sleep works the same way. It's perfectly possible for someone to push for 48 hours without becoming an invalid. I'd say minor penalties after 24 hours, crippling penalties after 48 hours.
- Illness creates very specific penalties, sort of like "reverse food". It may go away on its own, or it may escalate, resulting in more severe penalties. It can be treated at any point, but an advanced illness must be treated to be cured.
- Alcohol / narcotics / potions / stims provide either a.) a decent boost in one area and an equal penalty in another until it wears off, or b.) a massive boost in one area, followed by a massive crash in the same area when it wears off.
Aside from that, nothing about food or sleep will directly "kill" a player. It just adds color and flavor.