Circa 1987, DOS boot disk had a "Backpack" hard disk driver on it, so I could plug it in the parallel printer port and boot up with 300 Megabytes of my stuff instantly available as D: on on any customer machine. It made service calls a lot easier to manage, no more stacks of floppy disks.

300 Megabytes!!!

I had all my source code on it, archives, utilities, compilers, the whole shebang!