What items can be compacted into blocks?

In Minecraft there are several items that can be placed together in a 3x3 or 2x2 block to create a "block of _____". I've seen it done with Redstone, Coal, Wheat, and Lapis. What other items can be compressed into blocks so that inventory and chest space can be reduced? I have researched many times and always end up finding one or two new items. What is the full list of compact-able items?

Solution 1:

There are actually quite a few number of "compactable" blocks as of Minecraft 1.14.

For reference, some of these blocks are reversible, meaning that they can be turned back into 9 or 4 of the base material by placing them in a crafting grid or by breaking them.

Others are non-reversible, meaning they either cannot be turned back into their constituents at all, or else you receive less than 9 or 4.

Blocks crafted as 3×3 of base material

• Block of Coal (reversible)
• Block of Iron (reversible)
• Block of Gold (reversible)
• Block of Diamond (reversible)
• Lapis Lazuli Block (reversible)
• Block of Redstone (reversible)
• Block of Emerald (reversible)
• Hay Bales (block of Wheat, reversible)
• Melon (made of Melon Slices, not fully reversible unless broken with a Fortune-enchanted tool)
• Slime Block (reversible)
• Bone Block (reversible, made of Bone Meal)
• Packed Ice (not reversible, from Ice)
• Blue Ice (not reversible, from Packed Ice)
• Dried Kelp Block (reversible)
• Hay Bale (reversible, from Wheat)
• Nether Wart Block (reversible)
• Prismarine Bricks (not reversible, from Prismarine Shards)
• Purpur Block (not reversible, made from Popped Chorus Fruit)

Blocks crafted as 2×2 of base material

• Bricks (made of Bricks (item), not reversible)
• Nether Bricks (made of Nether Bricks (item), not reversible)
• Block of Clay (made of Clay (item), reversible when broken)
• Snow Block (made of Snowballs, reversible when broken with a shovel)
• Glowstone (made of Glowstone Dust, not fully reversible unless broken with a Fortune-enchanted tool)
• Sandstone (made of Sand, not reversible)
• Red Sandstone (made of Red Sand, not reversible)
• Wool (made of String, not reversible)
• Block of Quartz, (made of Nether Quartz, not reversible)
• End Stone Bricks, (not reversible)
• Magma Block, (made of Magma Cream, not reversible)
• Prismarine (not reversible, from Prismarine Shards)