Update the shop's setup to use ScriptableObjects to allow you to have more shop configurations or screens.

Expand the player's Inventory options. Change it to use a 2D layout, such as the shop, instead of using Unity GUI.

Update the Inventory items to have the type of inventory (weapons, armor, or potions) and then update the Inventory function of the player to assign different statistics for different items.

Think about extending the inventory system. Presently, if I buy two weapons, I'll get two slots of additional statistics (the same as if I buy seven swords). Obviously, you may not want to be affected thus, but how could you prevent it?

Have a go at adding money into the equation by making things cost money. In the purchasing section, display and act on it if the player does not have enough.

Put a second view in the shop to allow the player to sell items back to the shop.