Your spitz has taken the role of pack leader from you, he shows you that the objects (as you say caps, or toy etc...) belongs to him. You can correct him by follow the things below
1. You can eat in front of your dog but make sure you need to feed your dog after you eat only.
2. Growling is never accepted, remember you are stronger than your dog physically and mentally. Stay calm whenever he growls just say "Hiss(Snake Sound)" by pointing your finger towards him (Ceasar Millan Method).
3. Feed him only he is in calm state and never allow him to sit on sofas, beds or even dont allow to sit on your thigh too for long time.
4. You dont go near to your dog and pet, call the dog and pet him and even you are the one who should decide the time to pet not your dog.
5. In your house all things belongs to yours only so defend your property in calm and assertive manner and let the dog know the things are yours.
6. There is nothing wrong that you can growl to your dog if he growls.
Follow this, you might find some difference... remember dogs are clever creatures that can easily take pack leader position if the owner is weak in mentally. Be assertive towards your dog and stay calm.