Here is the back story for my project. (Ignore if you don't like boring "stories")
So i acquired 3 Dell Optiplex GX400 (pretty obsolete) desktops, after stripping it down bare to salvage parts i din't know what to do with the cases. Initially I wanted to toss them out for recycling but i thought I might as well reuse/upcycle it into something better. At the same time my summer break was coming to an end and I had to pack up my tools to be transported back to collage where I stay away from home. So it struck me to put one and one together and build a toolbox out of the old PC case. Its portable enough for me to transport between collage and home, and can be packed up into a really compact formfactor for storage or transport.

Build time: approx 20-30 hours over a few days (i took my own sweet time )
Materials:

Dell Optiplex GX400 case at MYR 5(bought whole computer as scrap)
Cardboard Calendar stand (free)
Mounting board x2 MYR 4
Mini Plastic Drawer x2 MYR 25 (entirely optional!)
Some fairly stiff but form-able wires (had them laying around)
Shoulder strap ( I got this free from an old bag rotting away )

Cost: About MYR(Malaysian Ringgit) 34 (thats like 11 USD) or about MYR 9 (3USD) if you don't buy the mini plastic drawers
Tools:

Scissors
Pencil
Ruler
Hammer
craft knife (xacto clone)
Staple gun

So here is a photo of it fully deployed and another of a some (about 80%) of the things i managed to fit in

With the vast variations of pc casings available over the years chances are yours will be quite different, in this instructable I hope to inspire you to breath new life into old "good for nothing" scraps and get organized at the same time. I hope that you would be able to get some tips (like the hook, it works really well) and ideas for your upcoming project.
Any constructive feedback is very welcome and if there is anything you wish to clarify, feel free to ask.
*your vote will be much appreciated too =)

Step 1: Power Supply Compartment

Alright the first compartment is made from an old calender's cardboard stand and is fixed to the case where the power supply was suppose to go.

The first thing i did was to modify the plastic tab adjusting/controlling how much to open it by propping it up.
I cut the channels deeper to allow it to move more easily.

Next is to build the box, I am really sorry but somehow i cannot find the pictures showing the build process. But basically you just need to make a box that is the size of a desktop power supply and attach it to the case as if it was a power supply.

Step 2: CD/DVD Drive Compartments

First start off by making some measurements, you want to know the length, width and height of the box you will be making.
The width and the height will be roughly the same as a DVD/CD drive and the length will be slightly more as it will allow us to use the space more effectively. Here I measured the length such that the box will go all the way in until it touches the "power supply" box

I made all three boxes out of mounting board, First you would want to cut the board to the right size with the dimensions of
(length+2*height)x(width+2*height)
Next draw the lines and score the lines at a distance of the height away from the 4 sides,
Then make a short cut from along the line until you reach where the lines intersect
(Please refer to the picture annotations for more detail/clarification)
You can now fold the tabs and staple it together to make the box
I attached mine to the original Drive holders with tape

Step 3: Hard Disk Drive Compartment

The hard drive compartment was basically a box that could swivel out.
There is not much modification needed.
I just hammered out some obstructing metal tabs and used the scrap mounting board to cover up any big holes
Then i just added a "door" with a handle and viola!

I made the door slightly taller so it would be able to close both the main compartment and the slot for storing paper/sandpaper/fabric

Step 4: Additional Compartment 1

This is a compartment i built that goes behind the "power supply" box and is only revealed when the "power supply" box is opened.
This allows the "power supply" box to act as the lid/door for the additional compartment.
It is a bit tricky as there is nothing holding it up initially and i had to add in wires to hold it

It is basically a cardboard rectangle held up by tape and wires.
Please look at the picture annotations for more detail.
However it is quite difficult to detail this process using words or pictures(apologize for poor pictures) and you would just have to go with whatever you can do depending on how the case is.

Step 5: Additional Compartment 2

This one goes under the "Hard drive" box and is basically a folded mounting board.
The box is made such that it can only be accessed when the "Hard drive" box is swung out, similar to the first additional compartment where it utilizes a moving box as the lid/door

Step 6: Hooks and Mounts

Here in an area beside the 2nd additional compartment, under the "Hard disk" box, i added a few hooks the can be secured and to any part of the fan grill.

The hook is basically a wire bent into 2 "S" shapes that are parallel to each other
remember to make one of the loops tight to ensure it fits securely on the fan grill

I also made a little horse-shoe-shaped wire that holds the staple gun to the floor of the case

Step 7: Mini Plastic Drawers

For the large empty space below the 1st additional compartment and "power supply" box I added 2 plastic drawers (majority of the project's cost )

This is very straight forward, I measured how much volume I have as empty space and went out shopping for something that fits well

Step 8: Final Step

To ease carrying the workstation/toolbox/pc around, I added a shoulder strap from and old bad

The strap is attached to the back at the padlock ring and I added some wires fixed to the front fan grill to attach the other end of the strap

Although the strap is attached to the bottom of the case at the front and back, it does not show any tendency to flip over as the straps are quite broad and grip the top of the casing

And thats all! we are done!
I hope if you are doing a similar project you would have as fun and fulfillment as I have