If it is a bike you may sell at some point, keep them to put on before sale. Example, I have Jones bars on my bikes, which I intend to use on future bikes. other examples pedals and so on. when I sell the bike, I put the original stuff on

If those are just crappy parts, like tires you upgraded, sell them. Some bike messenger or commuter always needs a $5 tire. Or use for a project bike, or donate to coop.