Accessories have always been one of the more expensive things for old Macs. It was pretty difficult to find accessofies on what my budget was in the early 2000s and late '90s, but it's been easier to find things like the EZ-135, serial cables, etc more recently.
The thing I would suggest is that not only does having these accessories make things easier--They also make things plain more fun.
Transfering data when you can set up a network or use bigger storage technologies like Bernoulli/Zip/EZ135/whatever (and although Zip is very common, it really doesn't matter what you end up using.)
Also, building up a small collection of things like this would make it so you don't need to dedicate an entire functional PowerBook to some kind of task like "being an external hard disk."