At least this wasn't that island that had Helios' extra special red cattle on it. There's no coming back from that...
[X] The buckler Leonardo made for you. It's not going to block Noble Phantasms or anything, but it's light and manoeuvrable and tough.
[X] Something from Astolfo's bag. He left it in his room like a prat and you can't shift it yourself, but maybe you'll get something good from the lucky bag?
[X] Rope. When isn't rope useful?
[X] Fourstam. He is your teacher and the leading authority on these things after all. Sure his vocabulary's distinctly limited at this point, but maybe he can still figure out ways to offer you advice? But then again, you'll never hear the end of anything he sees you do.
[ ] Rostam's shield. Heavy as hell for someone like you, but it's a magic-enhancer too right? With a piece of his Crest it'll probably respond. And if all else fails it'll take a beating.
I'm more inclined to bring this along just in case she manage to break Circe's curse, just so Rostam don't have to run all the way back to the beach. I don't know about her using it herself though. Doesn't inspire confidence purely by how unwieldy it is to Marche.
[ ] The rapier Leonardo made for you. You haven't exactly taken fencing, but it's not rocket science right? Stick them with the pointy end. Plus the other surprise inside.
Likewise this doesn't exactly inspire confidence. Stick to what you know or has a known (albeit still mostly untested) affinity for...
[ ] A grenade. Okay now you're really playing with fire but you know pirates had proto-grenades and if there's a problem that can't be solved with explosions you don't want to encounter it in the first place.
No playing with primitive fire gernade please. It's only fun until you lose a hand which is very likely considering who we're up against. Also the "I have a thermal detonator" trick never works.