This command requires 2 parameters:

• BagName - This is just the display name you want the exported bag to have. If the BagName contains spaces, you must enclose it in double quotes. For example: "Artisan Valley Bag"
• ModUniqueID - This is the ModUniqueID found in the manifest.json of the mod that you want to create a bag for. The exported bag will, by default, be able to store every JsonAssets modded item that belongs to this mod. If a mod contains multiple manifest.json files, then use the ModUniqueID of the manifest.json that corresponds to the JsonAssets part of the mod. For example, if you download this mod, you'll see that it contains several subfolders, that each have their own manifest.json. [CP] Artisan Valley, [JA] Artisan Valley Machine Goods, [MFM] Artisan Valley Letters, [PFM] Artisan Valley. In this case we would want the manifest.json in the [JA] Artisan Valley Machine Goods since this is the one that defines the JsonAsset items.
  

Suppose we typed the following into the SMAPI console:

generate_modded_bag "Artisan Valley Bag" ppja.artisanvalleymachinegoods

That would export a file that looks like this:

As you can see, this file is massive. But it's not too complicated, so let's step through every piece of data defined in it and what they do.

• "IsEnabled": true,
  

Possible values: true, false
This just tells ItemBags if the file should be loaded. Default value: true

• "ModUniqueId": "ppja.artisanvalleymachinegoods",
  

Possible values: Empty string (""), Non-empty string
This tells ItemBags what mod must be installed for this file to be usable. With it's current value of "ppja.artisanvalleymachinegoods", this file will only be loaded if a corresponding mod with that manifest.json UniqueID is found. This is optional. If you changed it to an empty string, ("ModUniqueID": "",) then the file would always be loaded.

• "BagId": "7a6fc755-19ce-b6e3-d6d7-445120a0fd45",
  

Possible values: Any valid GUID string
This is a GUID (Globally Unique Identifier) for the bag. You cannot have multiple bags with the same BagId. So if you generate multiple bags from the same ModUniqueID, then you will need to open the exported files, and make sure they do not have the same BagId. If they do, just go to this site: https://www.guidgenerator.com/, generate a guid, and use that as the BagId.

• "BagName": "Artisan Valley Bag",
  

Possible values: any string
This is the display name of the bag, not including the bag's size.

• "BagDescription": "A bag for storing items belonging to ppja.artisanvalleymachinegoods mod",
  

Possible values: any string
This is the tooltip description text when hovering over the bag, not including information about how many of each item it can store.

• "IconTexture": "SpringObjects",
  

Possible values: "SpringObjects", "Craftables", "Debris", "Tools", "Cursors"
This is the name of the Game texture that will be used to draw an icon to the bottom-right of the bag.
"SpringObjects" refers to the texture at "Content\Maps\springobjects.xnb", "Craftables" is "Content\TileSheets\Craftables.xnb", "Debris" is "Content\TileSheets\debris.xnb", "Tools" is "Content\TileSheets\tools.xnb", and "Cursors" is "Content\LooseSprites\Cursors.xnb"

• "IconPosition": "{X:0 Y:0 Width:0 Height:0}",
  

Possible values: Any Rectangle object that is part of the "IconTexture"
This is the position of the sprite within the "IconTexture" to use when drawing the icon. Typically this should be a 16x16 region of the texture.
Icon example:

• "Prices": { "Small": 2500, "Medium": 8000, "Large": 28000, "Giant": 85000, "Massive": 400000 },
  

Possible values: Any non-negative integer
These are the default shop prices of each size of the bag. There MUST be a value for each size ("Small", "Medium", "Large", "Giant", and "Massive"). Note that these prices are also affected by various values in the config.json file, such as "GlobalPriceModifier". For example, if the config.json file has "GlobalPriceModifier" = 1.5, then the Massive bag would cost 400000*1.5=600000 gold.

• "Capacities": { "Small": 30, "Medium": 99, "Large": 300, "Giant": 999, "Massive": 9999 },
  

Possible values: Any non-negative integer
These are the default maximum quantity of each item that can be stored in each size of the bag. There MUST be a value for each size ("Small", "Medium", "Large", "Giant", and "Massive"). Note that these capacities are also affected by various values in the config.json file, such as "GlobalCapacityModifier". For example, if the config.json file has "GlobalCapacityModifier" = 1.5, then the Massive bag would be able to store roughly 9999*1.5=15000 of each item inside of it.

• "SizeSellers": { "Small": [ "Pierre" ], "Medium": [ "Pierre" ], "Large": [ "Pierre" ], "Giant": [ "Pierre" ], "Massive": [ "Pierre" ] },
  

Possible values: The expected shop names are "Pierre", "Clint", "Robin", "Willy", "Marnie", "Krobus", "Dwarf", "Marlon", "Gus", "Sandy", "TravellingCart", "Employee" (This is the JojaMart shop), "HatMouse", "Khadija" (this is the shop from PPJA - Khadija's Recipe Shop), and these shops from Stardew Valley Expanded: "Sophia", "Bear", "Alesia", "Isaac"
These are the names of the shops that will sell each size of the bag. There MUST be a value for each size ("Small", "Medium", "Large", "Giant", and "Massive"). The value for each size is a list of shop names. For example, you could use "Small": [ "Pierre", "Willy" ] to make the Small size of the bag sold by Pierre and Willy.

• "SizeMenuOptions": { ...
  

These are settings that define how the bag's user interface should be laid out. There MUST be a value for each size ("Small", "Medium", "Large", "Giant", and "Massive"). Each size's corresponding value will look something like this:

• "Items": [ ... ]
  

Possible values: A list of items
This list defines some basic data about each item that the bag should be capable of storing. Each entry in the list defines data that looks something like this:


You can also specify a value for the "ItemCategories" property to define a bag that can store any items belonging to specified category Ids (requires ItemBags v3.0.11 or later). This property expects a list of integers for each bag size. For example:

"ItemCategories": {
    "Small": [-5],
    "Medium": [-5],
    "Large": [-5, -6],
    "Giant": [-5, -6],
    "Massive": [-5, -6]
  }
This would allow storing all Eggs (category Id=-5) in small and medium bags, and all Eggs and Milks (cateogry Id=-6) in large, giant, and massive bags. (Category Ids can be found at: https://stardewvalleywiki.com/Modding:Items). If "Items" AND "ItemCategories" properties are defined, then the result set is unioned (it will include all items of the specified categories, and all items that were explicitly specified in the "Items" list)

EDIT: For even more control over the items the bag can store, you can use ItemFilters, described here

If you use the generate_modded_bag command, you'll notice that the exported file contains all JsonAsset "Objects" and "BigCraftables" items belonging to the mod that the export was created from. But modded bags can store more than just that.

You can store:

• Json Assets - Objects and BigCraftables
• Content Patcher - Objects and BigCraftables
• Vanilla game content - Objects and BigCraftables
  

Basically, MOST items are "Objects", and "BigCraftables" and a sub-classification of "Object". So you can store almost any stackable items that exist in the vanilla game, or that were added through Content Patcher or Json Assets. Items that you CANNOT store are generally things like: Equippables (Hats, Boots, Rings, Weapons, Clothing) and Tools.

Here is the full item hierarchy used in Stardew Valley:

From the above list, any Item classified as "Object" (but not sub-types of Object (with the exception of ColoredObject)) can be stored inside modded bags. All you need is the name of the item, whether or not it's a "BigCraftable" (objects that can be placed on a tile of the game world, typically these are just machines like Furnaces, Recycling Machines, Cheese Makers etc, or other place-able objects like Scarecrows or Sprinklers), whether or not the item is obtainable in multiple different qualities (Regular/Silver/Gold/Iridium), and the size of the bag that you want to be required to store the item.