Here's what I have so far:
Eggbug Gluttony: If you kill an Eggbug and discover that there are too many eggs to eat, you can make bringing them back to a shelter worth your while. Combine the leftover eggs with loose rocks to upgrade them into Noodlefly eggs. After hibernation, each egg will hatch 2-3 baby noodleflies, each of which gives 2 food pips when eaten. An investment in two eggs will result in 8-12 pips’ worth of noots!
Gooieduck Enhancement: Using a mushroom, you can convert lots of items into nutritious gooieducks. Spore Puffs, Beehives, Blue Fruit, Jellyfish, Eggbug Eggs, Lillypucks, Glow Weed, Batflies, Dandelion Peaches, Centipedes and Vulture Grubs can all be crafted into gooieducks. Using a spore puff instead, you can convert Mushrooms, Grenades and Bubble Fruit into gooieducks.
Grenade: Combine a rock and a cherrybomb to get a grenade in a hurry. You can also add a rock to some batnip to get a cherrybomb.
I'll cut off my findings here; I just unlocked some very old and very valuable archives!
In my Rain World Materials photo library, I have an exhaustive grid of all of Gourmand crafting recipes. I've taken note of some useful recipes, so I'm going to convert them into a more visually friendly format and share them here.