The toolbox is dependent on what your doing..

If only for your self:

You need the hardware to get you up and running (without investment in a whole pc).. spare mouse, keyboard, cr2032 battery (ok more a tecks tool kit), power lead, phone lead .. these could be new in packets.. perhaps a 2nd hand (tested) FDD, and or a CD rom..
These all just incase a failure.. you have the starting points to test, or get yourself backup.

Software tools: you need the software to recover from the malware attacks.. clean the system.. or even system restoration softwarre.. that is restore from backups.. (we do keep out data on a seperate HDD or partition) .. I have seen various recommendations for these sftware tools..

Now If your planning on helping friends, or doing PC repairs as a second income or professionaly..
Hardware: a complete PC in Spare parts..hmm I joke..
in my situation:
CDROM, FDD, 40G hdd, CD-RW drive, Various Ram sticks, ATX PSU and assorted leads including USB, audio, PC/Molex Power, PS/2, IDE, SATA, Mains power, powerboard. a PCI and a couple of cheap AGP video cards, a x1 and a x4 .
This was built up over time.. and the devices used most will vary with time of year .
Some of these are for testing, some as replacement parts.. I normaly keep an old 20Gb hdd for data backup, drive imaging, testing
In the kit is 2 Digital Volt meters and an analogue Multitester,. the Analogue meter is for current testing .. watching for changes that the digital ones miss..
I recommend only a cheap DVM for starters that is what one of the digi meters is.. You will want at some time to kick start a PSU and check for life.. or test for Juice from the wall socket..boy the number of faults caused by lack of the Mains juice..
A cheap 4 port Hub, and network cables..

Software: CD's, Floppies, and USB drives

Drivers.. disks and disks of drivers... you have a clean install or called in after a clean install and some dodgy hardware.. leeching driver sites, copying driver cds has paid time and again..

OS disks.. Yep saw some one else with this.. You need these for repairs warm instals.. BTW.. if the Product key is not there.. ASK to sight it.. dont be a party to piracy..
CD's with patches, updates, Service packs.. regardless of the internet connection speed, a cd update is quicker than downloading .. and less risky

Live CD OS:
My current prefered is BartPE.. more because it is windose, we are able to get tools to edit the registry.. use other malware scanning tools.. Hirens boot CD is my second choice.. HDD tools, HDD regen, an extra AV source.. Partition tools, etc

Knoppix, FIRE, Plack.. tried each of them.. they are ok.. esp for file recovery, and spotting that hidden (even from BART) file that belongs to the new virus

General software: NTFSDOS.. you will need to run a dos utility on a dead NT machine.. I cried at the inital cost.. but it has paid for itself several times over now..

All the Adware/Spyware utils,

Virus Removal tools.. leeching Symantec, AVG, F-Secure and others helps.. some times one tool just wont clean it.. generaly Symantec tools 95% of time will ..

Boot Floppies.. just because.. some machines still need them.. in here I also keep the NTFSDOS boot floppies, some good ol'e dos tools including, registry tools mainly for 9x repairs..


And a well trained user..
read any and all pc magazine articals.. and question the comments.. some of those guys would learn a lot from this site.. Visit several online forums, you will wade through rubbish.. but the golden information is there..
Don't forget there are the hardware news sites, tech news,

Your education is the most important tool in the kit..
I have home crash test network.. this is for learning and is seperate to our Home network..
Having a machine that can be fiddled with is still a handy learning tool..

That covers some of my thoughts on this area.. oh and there are only 24hrs in a day.. the brain works best when some of the day time is spent with family and friends..

cheers