Selling immediately is the best solution for all of these. Think of them as supplementary income.
Note that working flight computers and power sources can be used for research/construction as well as having higher monetary value. This makes EMP cannons on your interceptors a good idea. Similarly, it's best to have fights outside UFOs and be less liberal with overwatch usage inside UFOs (in case they don't hit).
Earlier in the game, even things w/ research value like corpses and Elerium are also fair game for getting extra cash for satellites or other critical infrastructure. The only things I just about never sell are alloys and weapon fragments (useful for researching and constructing weapons/armor).