This is a mock UI for a fantasy RPG style game on the iPhone 5. My goal for this exercise was to give a convenient way for the player to buy large quantities of supplies with various item choices using the touch controls.
The solution I came up with was to touch on the left red squares to make a slider pop out and then drag it left and right to increase the quantity. The player can also easily scroll through the item list by dragging up and down, and the slider on the right shows the list position. After choosing all the items they wish, tapping on the Buy Items button will buy them all at once.