Here are some of my ideas:
Magic Beer: Peter, Quagmire, Cleveland and Joe find a treasure map in Peter's basement. It is a map that will lead them to the greatest beer in the world. They go on a road trip to find it. Once they arrive in Mexico where it is supposed to be, they find out it's guarded by a drunk Mexican. They easily beat him up and go to find a treasure chest. They open it, only to find the beer bottle empty. It turns out, the Mexican was drunk on the treasure beer.
The Evil Monkey Comes Out of the Closet: The Evil Monkey leaves the closet and goes out on a rampage through the city. It then is given a chemical that makes it giant, thanks to Stewie. But then, the monkey betrays Stewie and eats him. The rest of the town is dead as well except for the Griffins. They shoot at it, and it eats Meg. Peter starts cheering as Meg is eaten. Then Lois, Chris and Brian are eaten. Peter drops his gun and runs away. The Evil Monkey catches up and eats him. Peter finds himself in the monkey's stomach. All the townsfolk are there too. Then, they are blown out of the monkey's butt and the monkey becomes constipated. Then, it dies.
I know, they all suck.