I got hammered pretty hard by The Witcher 3 fans a while back for highlighting a mod that lets Geralt use shields—apparently, it's pretty common knowledge that Witchers don't bother with shields at all (I just thought he looked cool using one). So, it's with some trepidation that I'm suggesting another mod—this time, one that turns The Witcher 3 into a survival game by requiring Geralt to eat, drink, and manage fatigue. Hopefully, Geralt getting hungry and chowing down isn't counter to Witcher lore. If it is, I'm sure you'll let me know.
The Primal Needs mod comes with a small color coded display on your HUD to show you the status of your hunger, thirst, and fatigue, and there's a bit of depth to it besides simply eating and drinking every so often. Food expires within a few days, and while it will sate hunger it no longer heals as much as it once did.
The thirst meter depletes more quickly than hunger, but it's also refilled more quickly by drinking—and a dehydrated Geralt won't be able to regain stamina. Unchecked fatigue, meanwhile can make things more difficult while in combat, preventing you from sprinting, dodging, and blocking—and if you're really tired, you won't even be able to run.
These new needs, and the HUD, can all be toggled on or off individually, and the mod comes with a menu where you can tweak and adjust the settings for your needs to find the perfect survival balance. There's a lot more info on the Primal Needs page at Nexus Mods.