1. Play Army Attack
2. Open Cheat Engine
3. Select plugin-container.exe (firefox users) or chrome.exe
4. Scan current amount of coins
5. Keep clicking on Next Scan until only a few addresses remain
6. Click on the red arrow to edit all the addresses.
7. Select all the address (ctrl+A) and change the value to a higher value.
8. Now just purchase the item you want.
9. The game will get an error, but on refresh the item is still there.
10. Working and savable!