I am not sure about what files associated with my Multibit wallet need to be backed up (using Windows XP).
My current arrangement is that I have the wallet's data folder and .wallet file stored on an encrypted on-site USB memory stick. I use this on-site memory stick whenever I need to access my Multibit wallet. I have a second encrypted USB memory stick containing the same files that I store off-site. The off-site memory stick is for use if I loose access to my on-site memory stick.
When should I back up my on-site memory stick to my off-site memory stick:
- After every transaction?
- After every new receiving address is used?
- Never (the off-site backup will always be good for this wallet)?
My Multibit wallet is only used to receive bitcoins from my clients and to send bitcoin to my cell phone for normal spending.