The list is short right now, but it will be updated as new worlds and weapons are revealed for Kingdom Hearts III.
Locations
Big Hero 6
Revealed today during Disney's D23 expo, we learned that Big Hero 6's San Fransokyo will feature as a world in the game. Sora and pals will interact with the Big Hero 6 team after the events of the film, and Baymax will be there, too.
Tangled
Revealed during E3, the world of Tangled will appear in the game. We've seen Rapunzel's tower and its surrounding woods, but we don't know if we'll be venturing into the castle and its surrounding village or visiting the The Snuggly Duckling.
Hercules
Shown during E3 as well as during its initial reveal, but never explicitly stated by Square Enix or Disney, it appears Hercules' take on ancient Greece will appear in the game.
As evidence, we've seen Sora fighting Lythos the rock titan as well as exploring an area full of columns.
[Update] Twilight Town
Commenters have pointed out that this is in fact Twilight Town, as evidenced by the general aesthetic, the struggle poster, and the layout. Square Enix also confirmed it, so that solidifies things.
Weapons and Attacks
Big Magic Mountain
We've seen this attack twice now, both times fighting Lythos. It's worth noting that between its initial reveal and its E3 trailer, the, "Big Magic Mountain," in the bottom left corner disappeared. With the attack, Sora and pals ride a train through the sky swinging the keyblade as he travels.
Pirate Ship
Much like the the Big Magic Mountain attack, the logo in the bottom left corner disappeared between Kingdom Hearts III's first and second trailer. We've seen this attack used in multiple locations, which means it may not be enemy-specific, which may be the case with the Big Magic Mountain attack.
Mad Tea Party
Revealed at E3, this attack places Sora's crew in a collection of violent spinning teacups.
Two Shoot Blaster
We've seen the Two Shoot Blaster twice now.
You can shoot enemies with it.
This crazy Zeus weapon
Seen in Kingdom Hearts III's 2015 E3 trailer, it's not entirely clear if what you see above is a dedicated weapon...
...or just part of the transformation animation that leads to riding behind Pegasus in a chariot while you take out the heartless.
Master Xehanort's Keyblade
Seen briefly in the 2015 E3 trailer mounted on a wall perhaps as a trophy, it's unclear what is implied by its presence.