Sync your iPad to your computer as normal. This automatically includes a backup and gives you the opportunity to transfer any recent purchases made on the iPad. Go to Settings, Safari and Clear History. Also, go to Settings, Store and sign out of your account. You are now good to go.
When you get your new device just connect it to your computer and follow the prompts. When you get the choice you then select to restore from a previous backup which will be the one you just made during th last sync.