The island is a relatively easy place to survive. There are pigs inland, and fish in the sea (and Jin gets on with catching them early - he turns out to be a fisherman, which is handy), and plants. They get water too.

One thing that struck me, and not really wanting to get into the big Jack versus Sawyer issue, is that where Jack went through the plane wreckage looking for meds and alcohol that he knew he could use, Sawyer went through it looking for just about anything. After a while they set fire to the plane because it was becoming a health hazard, and then when they needed something Sawyer was the guy they had to go to. Eg I don't think he had any idea they'd need batteries from laptops, he just saved everything of value. Smart guy, who really helped the community.

I've not really looked at the tarps, but maybe some of them were material from the plane? Eg seat covers. (By series 2 they find other sources.)

I'm currently part way through series 5. Although there are good things about it, I'm not sure they are worth the bad. I'd say that 90% of the questions raised in the first series haven't been answered yet, after over 100 hours of TV. What's especially annoying is the characters lack of curiosity. They don't talk to each other, or share information, or even ask questions half the time. They'd been there a week before anyone even thinks to circumnavigate the island, and that's Syed who's actually just trying to kill himself, and he doesn't far. Had he continued, he'd have found the pier and other installations we see in the second series. For all they knew, there could have been a hotel on the other side of the island. They just didn't explore.