Buy an external hard drive.
Manually copy your data to it from your laptop.
When you get your new PC, plug the external hard drive in to that.
You could use an automated backup utility but I don't recommend that method, since you would need to use that same utility to access the backed-up files on your new PC, and there is always the risk that the utility may not be compatible with Windows 8 or future versions of Windows.
I have always used the tried-and-tested manual method of backing up my files (ie copy/paste or drag-and-drop).
Not only does it avoid compatibility issues, it also means you can access individual files from the back ups if you need to.
Automated backup utilities usually employ proprietary compression to create backups (to save space), so you might not be able to access individual files as easily as manual backups. Granted they may be more convenient (set it and forget it) but I don't trust them.