The 16K RAM pack that used to fall out when you had nearly finished coding
Yeah, I had the obligatory bit of cardboard wedged under mine.
My first overclocking experience was with a Pentium 200 MMX which I managed to clock to the uber heights of 225 which was all the motherboard would allow. I had more sucess with my Celeron 333 which hit dizzy heights and went to several of the early I series LANs.
My most expensive single upgrade in those days was a 3Gb hard disc which cost over £300 and was an upgrade to my 170mb disc. Back then folks I knew thought I was just throwing money away, after all how the heck are you ever going to fill a 3gb hard drive. I still have it and it still works.