Let's come up with some ideas to add to the shop for fun. I feel like what's in the game currently is fairly limited, despite how expansive it can be if you want to decorate your base. If you're not looking to decorate your base anymore, there isn't much to buy.
As an example, the machine category really doesn't have too much in the grand scale of how long the story mode is, considering you can probably have everything before you're even halfway through the story.
That being said, what would you like to be added to the shop?