Every PC builder should have:

[Rythmic]

You gotta hoard (though I think my three cupboards full may be overdoing it)

Gotta put done one of the most useful of all though:

A net connection!

[Dorza]

Grounding Equipment. Non magnetic srew driver, and little box of spare parts,screws etc. Thats what i take without fail

[da_ging]

knowledge without it even with every tool there is your still gona be screwed

[Barry]

Small power testing screwdriver, surge protected socket for every plug

[danbee]

My Cybertool. Couldn't live without it!

[Zak33]

good list guys

[steve threlfall]

Definately a very good quality magnetic screwdriver- makes evrything a whole lot easier. I find a little torch can help at times aswell.

[Zak33]

oooh...torch....bang on..cant live without it.

What about a little pot for screws..I use a plastic pot from some earbuds....when you drop stuff in it, the screws dont bounce straight out, for some reason. Works for me

[Blub2k]

a working pc with an internet connection for when things dont work to get to places like Hexus forums

[menthel]

Patience, an anti static wrist strap and a trusty philips head screwdriver. Oh and in my case lots of double sided tape for attempting to mount fans in unusual places!

[Lee H]

I've got a box with the following items in ;

2 x 56k external serial modems.
Spare memory
OLD CPU
voltmeter
screws, screws and more screws.
old cooler for current CPU in case of failure
old 350w PSU unit
a few leftover lights and cables
IDE cables
SATA cables
maglite torch
screwdriver with interchangeable head
OS backup disc with SP1a applied ( in case I loose the original )
A list of all my serial codes for various software programs
Disc with drivers and utils for system

[Big RICHARD]

Some pr0n, just in case you get bored with what you are currently doing and could do with a 'tommy tank'!

[funnelhead]

nice one richard. how about cologne - in case your working round a rich housewifes?

mm well since magnetic screwdriver is taken...

bootable ghost cd - so that once youve fixed it you can save your work

disk with spybot search and destroy, adaware, norton AV and zonealarm pro, all the latest updates and patches and all the little virus removing tools from symmantec eg for the blaster worm/ sasser

winxp and keychanger (the number of installations i come across using the blacklisted code is amazing)

most important

Blank cds to steal anything on their computer you like

[Rave]

Patience. I wish I had some, TBH. Overclocking your processor 50% straight out of the box to speed up the Windows install just isn't that sensible (it's worked for me so far though ).

Rich :¬)

[Howard]

Power leads.

It's the most annoying thing when one isn't included and you have to rummage in a box/ round the back of another PC to retrieve one just to switch the damn thing on.

[-mb-]

Anti-static bags, to rest components on, etc.

ATA cables with 3 plugs to cope with cheap PCs that have cables with only 2.

Jumpers, for when you drop and lose them.

Random converter plugs.

And of course, I second cable ties, screws and long-nose pliers!

Also,
SiSoft Sandra, Cacheman (for old PCs)
Adaware, Spybot, Syware Blaster
Any unified drivers for mainstream components
Standard MS fixes