For the most basic of needs:
1. 2.5" -> 2.5" -> 3-5" IDE cable
2. 2.5" HD at about 4GB will do it
3. IDE CDRom (and possible second 3.5" IDE harddrive for backup or extra storage)
4. 1Mb extra Chipmem underneath
5. PCMCIA 16bit 10Mbit Ethernetcard
And if you want to take it to the next level:
6. Silversurfer Clockport Addaptor
7. I/O, Soundcard or USB on Clockport
8. Turboboard with Fastmem (hard to get hold of so any will do but Apollo630/Winner630 is the best)
9. IDE Splitter, IDE Controller or IDE 2 IDE & SCSI Controller (Dataflyer 1200 SCSI or DataFlyer SCSI+ 4000)
10. External SD/FF
11. Graffiti external "Graphiccard"
