I used my paper route money to add storage to my Mac 660AV.

My options were a SCSI hard disk, SyQuest or a Zip drive. I went with the latter. Since it was SCSI it wasn't appreciably slower than the internal HDD so I had a disk with MS Office installed, disk with all my games, etc that I'd swap out for what I was doing.

I was happy with my choice a year later when SyQuest had gone out of business and I had 4x as much storage as I would have had with just buying a hard disk.

Three years later I suffered the click of death and I was less happy. I used some hack I read on Usenet about cutting off the outer 1mm rim of the disk with nail scissors which let me rescue my data.