Almost all the heart pieces I managed to stumble across just while playing and wandering round - the Zelda games have always leant themselves to exploration, and are full of little tidbits to discover. I ended up consulting a guide for 2 or 3 of them, though amusingly not the final one - it turned out that I'd previously skipped the one in Ikana Castle due to time. The remaining four pieces are on the moon and so I'll be getting them in the endgame.
That's the largest quiver, bomb bag and rupee wallet there, along with the Gilded Sword which I picked up in passing.
I never got close to this on the N64. Oh, some of the masks are trivial to obtain - the Bremen Mask you get just by chatting to Guru-Guru - but most are more involved, and the Couple's Mask in particular takes an entire 3-day cycle to collect (and that's assuming you don't screw up right at the end and have to go back to the first day and try again).
Unlike with heart pieces where once you're on the second row you've got plenty of hearts, it's worth going out of your way to get all the masks. Because once you've got all 23 of the ones in Termina, you can then collect the Fierce Deity Mask on the moon and absolutely annihilate Majora.
I'm sure the 7th bottle is new... but I'm not sure what it replaced (on the N64, like the 3DS, the inventory fitted into a grid). Maybe the Ocarina - wasn't that originally a C-button item?
Anyway, onwards and upwards!