All jetpacks and clothing items are added and removed from The Stash in a continuous cycle. It may seem difficult to recover them once they're gone, but it can be done! There is an "item cycle", which began with the 1.5 Update and which occurs every 22 weeks. During this cycle, two things happen: on Tuesday, there is an item (or items) on sale, and on Friday, there is a new or old returned item. Since the game gets its time from your device's internal clock, it is possible to set the date back to a cycle when certain items were available. This is known as the "Comeback Cheat".
1. Turn on airplane mode.
2. Turn off any kind of connection, including mobile data, Wi-Fi, Bluetooth and NFC. (android exclusive)
3. Go to Settings > Date and Time.
4. Set the date back to the cycle that contains your desired item(s).
5. Open Jetpack Joyride.
6. Open The Stash.
8. Purchase the item(s) you want, then return the date to its original setting.
The link below is a useful spreadsheet which contains all the dates for every item cycle and sale:
All pictures were done on Android device.