Well first off you really need a couple of external hard drives to backup your boot drive.
If you detest the corny and hobbled TimeMachine as much as I do, then you will likely prefer bootable clones instead.
So the clones will be GUID OS X Ext J formatted so OS X can boot from them, but the PC's can't read that format easily.
Also one shouldn't be taking risks moving their clones around and hooking them up to various malware infected PC's anyway.
Ok, next your going to need one or two external drives for transporting files between computers of different platforms (one backup), however you need to format this drive into something that the Mac and PC can read equally and with no trouble.
The formula is rather simple, take the portable drive(s) to the oldest version of Windows your using and right click and format the drive there for exFAT (not FAT, not NTFS)
Now if you have a XP machine and exFAT is not a option, then it can be downloaded for free from Microsoft's web site.
It's important to format the drive on the oldest Windows PC because XP can't read/format GUID partition maps and Vista and Win 7/8 can. XP uses a MBR partition map instead.
The Mac can read/write to all Windows partition map schemes and drive formats, except writing to NTFS.