I remember the family sewing kit. It was a big white plastic box with a tray inside. The tray had little slots to put your bobbins. There also were slots in the sewing cabinet drawer for bobbin storage. People were more frugal back then. A sewist probably had fewer than a dozen bobbins (I own 48 for my Janome Memory Craft 6500).
Back in the day, it was common to find a bobbin loaded with several different colors of thread. I mean, why fill an entire bobbin when you only need thread for a small job? So the sewist would add layer, upon layer of thread onto one bobbin. This isn’t the best way to manage your bobbins. Besides not knowing how much thread you have on the bobbin, the layers of thread can effect bobbin tension, thus effecting your stitch tension.
In my modern, less frugal life, I grab an empty bobbin and load thread on it every time I need a new color. Frequently, I don’t use all the thread on the bobbin, so I tuck it away for storage. Every once in awhile I realize I have a lot of bobbins with varying amounts of thread on them. I’ll also realize, that none contain enough thread to complete a job or they’re not the right color for the project.
My method of freeing up bobbins is to use them on my thread painting projects. In the photo you’ll see an example of the back of one of these pieces. Because I’ve set the tension right, the bobbin thread doesn’t peak through to the top so it doesn’t matter too much what color the bobbin thread is. I take a partially full bobbin, do as much thread work as I can until the bobbin runs out. Then I grab another one and use it up. I keep doing this until the project is done or I’m out of usable bobbins. There’s a lot of stop and go in this sewing process, but it is so helpful to clear up the partially-filled bobbin clutter. I also feel more thrifty because I’m using up what I already have.