It's easy to mess up sort orders when doing that, so take good notes on the categories you make.
Step 1: Create the "header" for the category of item.
Create a new item with the name of the category like "Poisons"
Go down to the Gear Type dropdown and select -New Tag-
- For the Tag Unique ID type something like XXPoisons Where XX is your initials or your Unique ID.
- For Name: type in Poisons
- Hit OK.
Select a Custom Gear Type Order (I suggest 15 or higher). Remember this number.
To the far right is a checkbox under the blue buttons that says Show Only? You will want to check that, this makes the header for you.
It Save and Test Now if you want it to go live.
Step 2: Items in the category Poison.
Create a new Item.
Under Gear Type select the tag you created above in step 1 (should read Poisons).
Under Custom Gear Type Order, choose the same number as in step 1.
Put in your other stuff like cost and weight.
Save and Test Now.
This should be all it takes. If you look in the Community Tomb of Annihilation (ToA) there should be a flora and fauna category that's set up the same way.
Every time you create a new Gear Type you'll want to make sure that the Gear Type Order is different. I suggest skipping 5 between categories in case you want to reorder categories later since they tend to cluster on the custom gear type order number tag.