If you only have one page, then concentrate on that. If you can deduce main themes from the text you have, that's fine. I think that, if you have been given RC landing on the island, then you should look at the descriptions of the islands in the two texts and compare them.
BTW- is this the section of RC?
http://etext.lib.virginia.edu/etcbin...&division=div1
IN RC, you have someone discovering a new worlds- one where money has become worthless, where the values are different from those he had before. In the Beach, you have an experienced person moving to a new island, but with a very diffeent eye, and with people around him who know the area. I'd look at that. Two islands, one writer, but two different stories.
Could you tell me exactly which part of RC you have?