Xie's Minecraft Hunger Mod
The hunger mod is a mod that adds a new survival dynamic to the game – the need to keep yourself well fed. The hunger mod is brilliant in its simplicity and gives you an actual reason to make a wheat farm, hunt wild pigs and generally provide for yourself even if you don't play in a word where spiders are continuously trying to fit themselves down your chimney.
The hunger mod works simply. It adds an invisible bar to your UI that has the same capacity as your health bar. When you start to run low on food, an indicator light will flash up to let you know that you're getting hungry. In the default install, the indicator looks like a little knife and fork.
At first, the knife and fork will be green, indicating that you should eat, but you're not suffering just yet. As you grow more hungry, the indicator will turn yellow and finally red. If you insist on abstaining from food, a skull will pop up above the hunger icon to indicate that you are now starving to death. The mod also has the effect of turning off health regeneration in peaceful mode if you allow your indicator to turn yellow. Eating is serious business, whether your world is friendly or not.
You feed yourself in the normal way, and each piece of food 'feeds' you as much as it would have healed you. So it's probably wise to build yourself a kitchen and familiarize yourself with in game recipes. If you get bored with the basic pork chops and cake, then I suggest checking out Nandonalt's cooking mods, which add a whole range of new foods to the game. Xie himself also has a pretty decent cooking mod that also adds a range of recipes, including stews, sandwiches and salads. His mod also includes new cooking blocks, including a purpose built stove. (So you don't have to cook your fish in the same place you smelt your iron.)
The hunger mod is configured to also work in SMP, which adds a new dynamic to the multiplayer experience. Check the download instructions before installing this mod if you don't wish to have the hunger mod function in SMP (let's face it, it's difficult enough to find a scrap of land to build on that won't get you banned in many servers without also having to worry about food.)
This mod is compatible with Mod Loader, and so should be compatible with other Mod Loader mods, including Xie's Farming and food stacking mods.