you should easily be able to get to that cave on a full lantern...no need for refills. What I did was warp past the mist area and backtrack. Makes it MUCH easier to get to that cave. It's the cave with a small chest on the bottom and two unlit torches beside it. You light both of them and the chest appears on a ledge above the small one.And yes, blow those little flower things up. One should be blocking a path with a treasure chest containing a piece of heart. There's also one in a room where you have to blow out torches with your Gale Boomerang, but I forget what room it's in. I think it had some of those tile worms in it though.
Oh, a note about fishing. You don't have to do it anymore in the story after the cat thing, but if you do it in certain areas you'll obtain another bottle and there's one place with a Piece of Heart that can only be snagged by reeling it in.
