I know I can backup the keystore files from my running ethereum client which holds my accounts.
But how can I backup wallets created with mist? Is it enough to write down the public address where the wallet contract is stored?
Go to the top bar and select
This will open a folder. Inside this folder there are keystrore files that have long names starting with
UTC--2016-04-14....... Each of these files represent an account. Back up these up.
Go to the top bar and go
APPLICATION DATA. This will open a folder. As far as I can tell, just back up this entire folder.
You could also manually add the wallet contracts back at any time, obviously, but this is easier and more convenient.
You want to store the keystore files in multiple locations & multiple physical locations. Keep in mind, you must prevent loss of both the keystore file and password due to loss or failure of you hard drive, USB drive, or whatever method you are using to back up. You also must keep in mind physical loss / damage of an entire area (think fire or flood).
For example, consider the add'l security of storing things in 3 places, over 1: - On computer
On a USB drive in apartment.
On a USB or paper at a trusted family member's house (e.g. with things like your birth certificate)
This way if your house burns down, you still have access to your funds. If your HDD crashes, your still access.
If you do want a paper option, you can import your Mist keystore file into MyEtherWallet (running offline/locally, see #5 here). Follow those instructions and use the View Wallet Info tab in order to access your Mist wallet and then print a paper version.
On some versions, (0.3.9) there may just be a BACKUP option in the top bar, not under accounts. For old versions (0.3.7 or lower) the backup option is simply not there.
Depending on what OS you have, you need to navigate to the right folder (below) and back these keystore files / the entire keystore folder up.
The above will only back up your normal accounts. Wallet Contracts can be manually re-added, or you can back up the data folder. As far as I can tell:
~/.config/Mist or, in earlier versions:
~/.config/Chromium/Mist (folder is hidden)
C:\Users\< Your Username >\AppData\Roaming -or-
The folders I see online tend to be all over the place. I can confirm that the above certainly hold true to my Mac.
Edit: I found this (possibly out of date) list for go (geth) and c++ (eth) clients which may be helpful for some.
If you use the latest version of the Mist wallet 0.3.9, then you can backup your wallet with saving the AppData. You can do that by clicking on Backup in the Menu bar and click "Backup App Data" which points you to the installation directory where your wallet is saved. In my case it is located here "C:\Users\Andreas\AppData\Roaming" on Windows 10 - 64 Bit.
Just copy the whole "Mist" Folder to a secure location to have a backup. In my case it has just about 6.4MB.
Now you have a backup. I cannot say if the same is true for Mac and Linux.
Greetings from Austria
To backup your accounts from Ethereum Wallet, see How to backup mist wallets?.
The files that you need to backup will have names like the following:
user@Kumquat:~/.ethereum/keystore$ ls UTC--2016-04-17T01-23-45.279405976Z--aaaaab3ad17cd9aca6fd5343a53a513685c7aaaa UTC--2016-04-17T02-34-56.029466208Z--bbbb8622d70f62f212aef64e7e26e4746dc8bbbb UTC--2016-04-22T03-45-01.402684763Z--cccc5fc7979143c593c6c01eae6d22b7d6eecccc
To restore these accounts, copy these files back to your Ethereum keystore directory. The location of your keystore directory depends on your operating system - here are the directories: