Collect water in the cup, plant the peanut and use the balloon as an s.o.s signal ;0)

I would look for a good camp site. I would eat the peanut. collect rain water in the cup. and blow up the balloon for a head and someone to talk to.

You could use the cup to dig further inland near a cliff base, if you dig a couple feet you may find fresh water...if this doesn't work, you need to go ahead and focus on building a fire. The peanut shell can be used as kindling to start a fire with since it will be dry and catch fire somewhat easily..peanuts are excellent fire enhancers..you don't have anything to make a spark with so you didn't mention the balloons color but filling a clear ballon with water and holding it up so the sun can shine through it will work like a magnifying glass and has been proven to work in the same manner and start a spark. Now you have fire... You can go weeks without food but only days without water so next step is to get fresh water. If it's a deserted island there may be coconuts but you don't want to eat them or drink the milk unless you have to, it is a diauretic and will give you diahrea...but you need a coconut..take the hollowed out coconut or some other item you could use as a bowl, then fill your cup with some sea water and place it above the fire high enough that it will not get too hot and shatter, next take your ballon and empty it out and stretch it over 4 sticks tied together with whatever you can (grass, soft bark, weeds, leaves etc.) find. You now have a square/rectangle frame with a rubber ballon steatched over it..place this above the cup at an angle. The water/steam coming from the cup will collect on the ballon frame and run down and drop off into your bowl..you now have fresh water. Next up is food, you still have your peanut, you only used the shell..go ahead and smash this into a fine peanut butter like substance and rub it on your nose and face as sunblock, you are probably gonna be exposed to more sun than usual and the peanut is not gonna be enough protien to do you any good if you eat it. Sharpen yourself a good stick (you can sharpen a stick by grinding it against a rock) and go spear some fish, crabs etc and cook them up in your fire, or go spear a monkey or something and cook it up. Kill a few monkeys and you can make yourself some clothes or something.... Now that you have food and water all you have to do is collect some leaves and such and make yourself a shelter...might be good to use you cup again and dig yourself a deep trench in the sand..one to poo in and one to make your hut over...the trench will be cooler and lend you more shade as well as give you more protection from wind, rain and animals.