Gelatinous Slime Drop
If you put a Gelatinous Slime onto a Drying Rack and wait 5 minutes, it will turn into a Gelatinous Slime Drop. The Gelatinous Slime Drop is a food item that restores 3 hunger when consumed.
Blue Slime Crystal
Gelatinous Slime, just like Green Slime, cannot be worked directly in a Part Builder. Instead, put into a Crafting Table 4 Gelatinous Slime, 1 Dirt, and 1 Sand to make 1 Slimy Mud. Then, cook the Slimy Mud in a Furnace to make a Slime Crystal. It is these slime crystals that are then used in the Part Builder.
Note that tool material costs are in terms of the Slime Crystals and that 4 units of the raw slime are required to make 1 crystal. So, to make a Crossbow Limb (Material Cost of 4) out of blue slime requires obtaining 16 Gelatinous Slime.
Congealed Blue Slime
Congealed Blue Slime is a block made from four Gelatinous Slime. It can also be found on floating Slime Islands around the "lake." It can be crafted back into 4 balls of Gelatinous Slime, again.
Slime Channels are used to make bounce pads. They can be used as a placeable water stream, and can be used in the Nether. This allows for Overworld-based mob farms that use water to work there.
This is very useful for starting because you can climb/fly up to the island so you can kill the slimes and get pretty much unlimited food and good tool materials!