What is the best software to have on portable HDD?

I just bought a portable HDD.
What is the best software to install on it?
My "plan A" is this:
Cut disk into 2 partitions.
On the first partition install some software to help me diagnose and fix my PC when broken (DOS software?)
Maybe some good LINUX compilation bootable from the portable HDD, with no installation required - to help me access my C:/, when i dont have the time to install or fix broken windows - or to help me learn linux when im bored
On the second partition i would keep everything else, like PortableApps, some kind of backup/synchro program, some movies, files, games...
So that when im at work i just connect my HDD to work PC and i have access to all my favourite software - like txt editors, gimp, and games.

PS also maybe some third partition for windows installer, so that when my windows gets broken and i need to reinstall, i just boot pc from portable HDD and installer starts (no need to burn windows on CD - i hate CDs ;/ ).

PS2 Windows installer partition & Linux partition on ONE portable HDD...some kind of boot manager required?

I just like to be prepared for any situation, to develop this concept to perfection, learn something in the process and for years to come it will make my life a little bit easier ;]