Combining Gears

Combining Turtle Helmet and other helmets to give them water breathing

Combining Leather Boots and other boots to give them ability to walk on snow powder

Combining Elytra and Chestplates to give them gliding ability

Recipes

Combining Gears at Smithing Table

Turtle Helmets as template, other helmet as base (1.21.1 has to add Kelp as addition)

Lether Boots as template, other boots as base, wool as addition

Elytra as template, Chestplates as base and Phantom Membranes as addition