Fire and more importantly Piggy's glasses. I guess you could also include Sam n Eric who Jack's group "capture" and force to join their tribe.
Sam'n'eric
Sam and Eric; the twins, also called Samneric in the book
The two boys who left Ralph's group to join Jack's group in "Lord of the Flies" are Sam and Eric, also known as Samneric. They were lured by the promise of hunting and adventure in Jack's group, which appealed to their primal instincts and need for excitement.
They took Piggy's glasses, and fire from Ralph's camp.
Jacks are for lifting or raising things. They can be screwed jacks or air jacks, or most commonly, hydraulic jacks.
Sam and Eric tell Jack that Ralph said he was going to hide near by so they go looking for him there.
THE GRAINS GROUP, SILLY!
Samneric
Ralph
one of jacks group throws a big rock off the mountain and lands on Piggy's head and dies.
The two reasons of why jacks group is more exciting than Ralph is because jacks tribe hunt and have a feast and have fun.
By creating a set of rules. After Ralph become their leader they create a set of rules, what/where the lavatory is, building shelters, fetching food, lighting the fire (fighting for rescue). This diminishes fast though. Also Ralphs group after the boys split combs their hair back (society influence tells you to do this) to prevent themselves from looking like jacks group (a pack of savages).