I wrote the first 10,000 lines of ROMlib on a Mac+ with no hard drive or even a second floppy drive. I had Think C on multiple (IIRC, five) floppies and enough room to have a few portions of ROMlib and tests on the rest of each of the floppies.
Backups involved copying floppies, which was a bit time consuming with only a single drive.
Good times!
(ROMlib was my clean-room reimplementation of much of System 6; it was a big part of Executor [0])