Numerous trees can be used for self bows using a single piece of wood.

During their excursion they will probable try to make a self bow. Is a good option for hunting big game. If thy want meat they will have to figure out functional weapons they can make with only a knife.

A self bow is a bow made from a single piece of wood. Extra material such as horn nocks on the ends, or built-up handles, would normally be accepted as part of a self bow.
In many parts of the world including much of Africa, the Americas, northern Europe, and Southern Asia, the great majority of traditional bows are self bows.
A bow is an ancient weapon that shoots arrows powered by the elasticity of the bow. Energy is stored in the limbs of the bow and transformed into rapid motion when the string is released, with the string transferring this motion to the arrow. The bow is used for hunting, sport ( target shooting ) , and in historical times was a weapon of war.

Check out the survival facts on how they intend to go about it.