The first of these three since I think minecraft is missing these, are more shields, a few of the ones I thought of:
iron
Gold
Diamond
blaze- low block, shoots fire while blocking
Glowstone- low durability, high block, illuminates the area
reinforced glowstone- made with obsidian and the previous shield, has higher block and durability
Mirror- made with the reinforced glowsone shield and 8 rare materials, has very high block, illuminates area, and deflects projectiles.
emerald- makes enemies stronger and harder to kill, but they drop crafting materials and rare materials.

second mod:
a leveling system that works by crafting a statue, making a shrine for it with 9 wood as the base and 2 flower pots with any plant in them, but you will trade 10 emeralds for 5 hearts, until you get 20, then you will get different colored hearts over the previous hearts in this order: gold, purple, blue, green, and orange. emeralds would become much rarer in the "overworld."

the third would add more materials and armor types as well as more realms, especially ones with larger amounts of emeralds (giving incentive for the other mod) and having enemies that have higher chances of dropping them the harder they are, also adding a spell system would be nice, and have a devotion for players to a certain type of magic: healing & holy, fire, dark, lightning, and ice.