What syncing services have you enabled for iCloud syncing?
Contacts & Calendars have the option to 'export archive' in each of their File menus, do that & you get a copy of the data for safekeeping. When you disable these two services in iCloud you can restore from those backups (without using iCloud again).
I'd also suggest you take a full bootable backup or ensure a Time Machine backup is up to date (a clone seems easier to restore to me). If anything goes wrong a backup may be the only way to recover once it is deleted from the iCloud servers.
Other services may require you to take copies in other ways, e.g. ensure iPhoto has local copies from the photo stream. Move any Documents out of iCloud Drive if you want to stop using that. I would also duplicate ~/Library/Mobile Documents/ to another location to get a second copy of files in iCloud Drive.
Apple have this explanation for 10.9, but I can't see a new one for 10.10. Perhaps if you disable services individually you can keep the local copies?
OS X Mountain Lion: Start or stop using an iCloud service on your Mac