Most people think of what would keep you alive longest but you should really be thinking about what will get you rescued quickest, so small items like a mirror for signalling or a flare gun would be top priority.
Depends if you want to be rescued or not though... might be a really nice island ;D
Think the 5 C's Oisin posted is a pretty sensible list. Think I would make the cutting tool something like a Leatherman with a few handy tools. Firesteel for fire lighting (although I'm hardly stellar at lighting fires with one!). Tarp for sleeping under and will swap the water container for hammock in the hope I can find a coconut to use as a water container or something ;) Paracord sounds fair enough for the last item. For entertainment I would have to fashion the infamous "cup and ball" toy using the aforementioned coconut, paracord and something scavenged resembling a ball :D
(http://upload.wikimedia.org/wikipedia/en/1/1a/Ballinacup.jpg)