Well I am at home now so have the CD-R in front of me.
The "Demo 16M" folder is Akai's factory demo for the MPC4000 (~16MB in size) - it's in that cheesy jazz-muso style that I'm sure we'll all groan at.
It's got a multi, a bunch of programs (drums, piano, bass, strings, thunder...

and a sequence to play them.
The "Drums" folder has a few kits in - they're all fairly pristine and recorded (on an MPC4k? I dunno) with clarity... not quite my bag, but I guess it's always easier to scuzz up a clean sound than it is to clean up a grotty one.
The "GM Sounds" folder has samples for the General MIDI stock sounds, both drums, keys and instrument sounds. If you really need that General MIDI "goblins" patch well here's on for you...
The "Keyboard sounds" folder was the one I found the most useful -
it's got some very usuable Wurlitzer & Fender Rhodes electric piano samples, a selection of MiniMoog and ARP Odyssey ones, a Hammond B3 and an acoustic guitar.
If you're an analogue knob twiddler like me, you will scoff somewhat at static samples of a Hammond or a minimoog, where you can't tweak the sound like on the real instrument, but nonetheless, these instruments sound so good that even a static sample of them can be musically useful (and you can modulate it more with the MPC4000's sampler engine) -
the "miniMoog No.9" one a rather thick 3VCO unison blast that I've used myself on a few tracks. The Wurlitzer too.
Finally the "Thunder" folder seems to just be the same thunder that is already in the "Demo 16M" folder, the fact that it's duplicated at top level just to me showed the sort of shoddy arse-from-elbow guff that was going on at Akai back in 2002....
On my 4K's harddrive back in 2002 (UK retailer), I also got:
- "24 bit drums" - the only samples that were actually 24 bit in the whole library!
- The Akai S5/S6k Vol1, 2, 3, 4, 5, 6, 7 and "spendid piano" and "splendid drum" libraries.
- the "MPC Vol. 1" library that came with the MPC3000XL, which includes all the factory sounds for the MPC60, MPC3000 and MPC2000.