See the box at the top right corner with the title "Inventory"? That's right, that is what you are carrying with you at the moment.
Using the Inventory Box
The only use of the inventory box at the top right corner is to see what items are on you, and how much empty space you have left. Hovering the cursor over an item will show the name, description and additional information (such as Broken...). It is not possible to use any of the items through that interface. To use an item, scroll down to the main interface for the options.
Capacity For Residents
A Resident may carry up to 4 objects in their rucksack, while the Town Uniform takes up a 5th space and cannot be dropped. All Professional tools provide an additional space for themselves and cannot be dropped and so are usually ignored when talking about backpack space.
Capacity For Heroes
Capacity Increasing items
Carrying certain items will increase your maximum backpack space, although they themselves take up one space (the minimum space provided is +2 spaces, for +1 net free space).
- Utility belt adds two extra spaces, for a net total of one extra free space. It is the only item that will stack with the other containers below.
- Manbag adds two extra spaces, for a net total of one extra free space.
- Ultra-Rucksack adds three extra spaces, for a net total of two extra free spaces.
- Shopping Trolley adds three extra spaces, for a net total of two extra free spaces. Note that this is a Heavy object, so no other heavy objects can be carried.