Spare parts for fixing and embling pc's?

My bf likes fixing computers, actually he loves it. If i were to buy him an embly of spare parts for his birthday what would you geniuses recommend? cuz i have no clue, im just brainstorming. i dont even know whether its a good idea for a present or if its not necessary...lol idk. any comments, suggestions, encouragement, recommendations ect would be helpful :) thanks