Here is my take:

Your first priority is to make it to the island alive. Flotation is #1 if you can't swim the distance.

Once you arrive safely, you probably would have a difficult time living there for a couple of years (think Tom Hanks in "Castaway"). So, your #2 priority should be getting rescued. The mirror is your best bet for this. You stand a chance if making fire using natrual materials ("Castaway" again). You stand NO chance of improvising a mirror. A signal mirror can reach out 10 miles on a good day. So, to me, the signal mirror is your second priority.

You have the army survival supplies listed as #2. At some point those supplies will give out and you may die. Once again, your best shot is to get rescued, so these are less important than the mirror.

Without water, you can live 2-3 days (maybe less if you swallow a lot of salt water). So the water would be #3, to me.

The plastic sheet would be the next priority. It can be used for many things, including water collection (depends on the weather, though).

Cordage should be next. You can improvise with vines, but real cord is better.

Fishing kit would be next (at least to me).

Of course, this assumes that you are not using some things to float other things, as others have suggested. If you can float the water and fuel, and use the cord to tie those things together, then of course you should take whatever you can.

My priorities also assume that somebody will miss you and be looking for you. If this is NOT the case, then some things might change.