Here's my theory for whats in the hatch:
Turns out the "Others" are a group of Colombian drug cartel enforcers/grunts. They're on the island growing cocaine and marijuana, which they just so happen to be doing underground, otherwise they might have a "The Beach" situation arise. Hence the light from the hatch. I think when Kate goes down into it, she accidentally tripped the timer which controls the lights, hence them turning on, but it shorts due to the explosion. So it turns back off. And...uh...then...um...they all go into the hatch and get ripped. Yeah, thats it. Then, Cheech and Chong show up with the resurrected Timothy Leary, and it turns into a psychedelic party for all. And it turns out Leary has been on the island the whole time, adding LSD to the water supply, hence everyone's trippy experiences and stuff. They all get the munchies and eat all the food, and from there on out slowly starve to death in a drug-induced haze as they're too lazy to go hunting and gathering for food.
The moral lesson: drugs are bad. But alcohol, cigarettes, and prescription painkillers are still ok.
THE END