A simple and safe method to save/restore virtual money and goods?

[Broken Stylus]

You have the minimum stuff: access to Asset Store (billing services) and Game Center. The game is fairly simple so the architecture to sustain it should too.
The solution must not require setting up a third party server account, nor depend on iCloud.
Intuitively I'd say it's nigh impossible but maybe I missed something.

Data to be saved :

1. Virtual currency (VC), a given amount, bought with several options of IAP (small spending, medium, big, etc.).
2. Some virtual goods (VG) bought with VC (not IAP!).

The VG are non-consumables and can be upgraded too (think of weapons).

How would you proceed to allow such data to be saved so it could be accessed and restored on another device?

If there is really no quickly available option, should we strongly encourage the player to use an iCloud account to save this data (I currently am able to save keys that point to string data)?

[Thore]

If players save the file, and restore it later, and there is no server-side oversight, expect players to tamper with the file and cheat. As long it’s strictly single player, it might be barely permissible, but if actual money or any kind of multiplayer (even indirect, hiscores etc) is involved, I strongly advice against such solutions.

[Broken Stylus]

Surely you don't want this to be entirely local, obviously. I was trying to find a way to save that kind of data without going for a third party server. Trying to find a work around by using Apple's native services without already relying on iCloud (not everybody uses an iCloud account).
I've read some people try to use "buy x gold" options as restorable to keep track of how much a player has spent to acquire gold (or gems, or anything like a virtual currency). But I thought you could only have one single receipt per buyable item (in this case, small, medium and big bags of gold coins for example). Secondly, that wouldn't account for the virtual currency won by playing or by watching ads.