The first thing you need to get is get a glitch called walking while talking with an item drop. To do this you need to pick up an item drop like deku seeds, deku nuts, deku stick, magic jar etc. for the first time while the camera is messed up, either quickly after exiting a crawlspace or when being revived by a fairy while in the water (and preferably out of bounds). You then need to get hit by an enemy to be able to move around, and you should have the item pickup stuck above/inside link. Once you have this, the next time you enter the water you will get an item. You can manipulate what item you get by walking in front of a chest which changes this value. So just walk in front of a chest with the value you want, jump in the water and you might get something cool. The 2 big things from this so far are light arrows with a recovery heart chest, and a bottle with blue potion from a map chest.