Some people like to collect things in their spare time. Personally, I have never understood how that constitutes passing the time. Creating things, useful things, is a bit more rewarding. For those that want to do something constructive with their time a book binding hobby might be just the thing.
Effectively putting books together can be great. You are able to do something productive while at the same time finding comfort and relaxation in the efforts. Book repair or restoration is another similar activity that can also be tied into it. It can also be valuable. If you want, you could list what you do in the paper or on an auction site to see what you are able to get for it.
A very productive pastime is sewing. Be your own designer and make your own clothes. You could be absolutely sure that everything fit correctly. This is really great if you have a hard to fit sort of shape. You can even find ways to extend this to household items such as pillows, or draperies. Best of all no one will have exactly what you have so you can be assured that it is all one of a kind.