Upon waking up on the island, Claire mentions the rule of 3 for survival: 3 minutes without breathable air, 3 days without water, and 3 weeks without food. There is a fourth rule that she leaves out, 3 hours in a harsh environment. If you find that you have become lost, the first rule is to stay put. The average person is found within 48-72 hours after becoming lost. The second is to treat any injuries. The third is the find or make a shelter. The fourth is to build a fire. The fifth is to signal for help. The sixth is to find drinkable water. The seventh is to find food.
Father Fogden offers Claire some Yupa to smoke with him after dinner. Yupa plants and their seeds are ground and smoked; the seeds in particular are an hallucinogen.
Bum rolls worn in the 1700s were often stuffed with cotton and/or rags, either of which are good materials to help start a fire.