Inventory

From Harvest Moon - Wiki on Neoseeker

You can access your inventory by pressing the + button. Your inventory displays your items, money and equipment.

Items

In Rune Factory Frontier you automatically have a wide space in your inventory to store your items. Each item has a level, 1 being the lowest, 10 being the highest. Some items have only one level, such as runeys. The higher the level, the better the item is and the more it is worth.

Most items can be stacked up to 99 per box. If 2 items are the same, but can't be staked together, they are probably in different levels. Note that weapons and Tolls can't be stacked together.

Money and Shipping

The amount of gold that you have is displayed in the upper-right corner of the inventory menu. To earn gold, look into the shipping box at the western side of your farm. Your inventory and the shipping box will open. You can transfer the items from your inventory into the shipping box by dragging the amount of items over into the shipping box, which is on the right side of the screen. The amount of money you earn appears at the bottom-right hand corner.
Rosetta will pick up your items at 5:00 and you'll earn your money then.

Custom

You can open up the custom menu by pressing +, then + again to switch the screen. You can customize your shortcuts here, making them easier and quicker to use during gameplay. There are 2 places you can customize using custom.
4 spots are used for storing food and medicine for quick and easy access while you're fighting in dungeons. You can use theses items by pressing the D-pad on the Wii remote.
8 other spots are used for placing tools, seeds, weapons, etc. By pressing - while in normal gameplay, the items you've set here will appear first, and save you time looking for them.