When you first start your adventure in One World, the storage bag only had room to hold 3 items. Before you leave home, Mom will upgrade your Hand-Made Bag to hold 14 items. With the rucksack divided into two halves - Bag and Important Items - your tools and other devices won't take up item slots.
To access the contents of your bag, press the Y button (Nintendo Switch) or the Square Button (Playstation). You can sort the items in your bag by pressing X or Triangle. You can hold a stack of 99 of each unique item in your bag.
As you proceed through the game, you'll soon find that having only 14 bag slots isn't very convenient. When your bag is full, any crops or animal products you harvest will fall to the ground (until you can pick them up later), and you can't collect seeds from Harvest Wisps. Luckily, you can expand your bag to hold more junk, thanks to Mom. You don't have to raise her friendship level or bring her materials for crafting. Mom's upgrades will become available as you increase the percentage complete in the encyclopedia and as you complete the game's story.
You can find the blue encyclopedia book inside of your farm house. The book's completion percentage is located in the upper-right corner when you open the book. An entry will be added to the game's encyclopedia when you find a new crop mutation, animal, fish, cooking recipe, and mine ore. There are a total of
- 231 crops and flowers (241 if you have the Far East Adventure DLC),
- 65 farm and wild animal (92 if you have the Far East Adventure DLC, the Precious Pets DLC, and the Mythical Animals DLC),
- 30 fish,
- 330 cooked recipes (358 including the recipes added with the Far East Adventure DLC), and
- 42 ores, raw gems, and processed ore/gems.
Completing the story requires you to help the local towns with their problems. Once you do, you'll be rewarded with Harvest Sprite medallions. The first town, Calisson, needs to be complete before you can expand out into the world. After that, you can solve the other four towns' problems in any sequential order. There are a total of six medallions.
If you ever lose track of your bag upgrade progress, Doc Jr will contact you through the DocPad when you've met the requirements for a bag upgrade. He'll remind you to return home and visit your mom.
Bag Upgrade 1
After you have you have collected 2 or more total medallions and your encyclopedia is at 5% or higher, return to your house to visit your mom. Talk to her inside of your house to have your bag expanded to 7 more slots (total of 21 slots).
Bag Upgrade 2
Now you'll need to collect 4 or more total medallions and your encyclopedia is 10% or higher. Mom will then give you a High-Quality Bag with a total of 42 slots!
Bag Upgrade 3
The last upgrade is available after you collect all 6 medallions and complete the main story. Your encyclopedia must be 15% or higher. Go talk to Mom again to receive the maximum-sized bag with 63 slots.