I had a bit of a hard time differentiating between text and background. I like the art, and i like clicker games, but i also would've like to have some "noise" or visual kinda of juice as to when I clicked a button.
Finally, when i first open the cart, and buy something, I did not realize the tray was still open. So my play area was just blank, and I had to click around to the top of the cart to actually close it and get back to the game.
nice idea though, especially for count down.