Catcoons will take the following items if they are on the ground but won't accept them as trade (they have one of the eligible tags for ShouldAcceptItem in catcoon.lua).
I don't know which ones are intentionally not supposed to be tradeable and which ones are. I've listed them based on their prefab name in the prefabs folder
- halloween_ornaments (none of them)
- moonbutterfly (they do accept a live butterfly and moonbutterflywings though)
- oceanfishingbobber (none of them)
- tallbirdegg (b/c they lack the tradeable component, you can't give it to pigs or pigking either, whether it be cooked or raw)
A common theme is that they are missing the tradeable component to them.
Use catcoons for a trading project. Notice that some items that the catcoon could be accepting cause they have the eligible tags in ShouldAcceptItem in catcoon.lua also lack a tradeable component.