The items of clothing don't all have to be in your inventory at once. They just need to be saved into the encyclopedia. You will most likely get this eventually when going for all the girls' routes, but if you want to grind it out, take out the camera in scan mode and scan civilians. It will show you the names of the clothes they're wearing. If you have that item registered in the encyclopedia, there will be a little book symbol next to it. If there isn't a book symbol, initiate a fight with the person by pressing O and pushing them. They will either run away or fight back. If they fight back, strip them and hope you don't rip the item. If they run away, don't worry as you will most likely come across someone else with that same item as there's not too many different types of civilians in the game. After your first playthrough you shouldn't have to worry about ripping clothes that much.