The Stash is where you can store Tools and Resources. After you initially repair the stash at the beginning of the game, you will find the Axe, the Trowel, and a stack of 4 tomatoes inside of it.
When you Use the stash, you will be presented with a window. This window will show slots for your Tools and slots for your Resources. Your stash can always store up to 4 Tools at a time. At the beginning of the game, it can store 2 stacks of Resources.
Upgrading the Stash Edit
You can upgrade the stash. Each upgrade changes the appearance of your stash and the number of Resource storage slots, up to the maximum number of six slots.