In his opinion nearly anything is good to have lying around. He is secretly just a very proficient pack-rat; although it might have been easier to hide this trait in the TARDIS, where there was quite a bit more room. As it stands he probably just has slowly been accumulating little things everywhere in the flat.

'Good point. Maybe I ought to just keep it indefinitely.'

He can be possessive over people as well, it just takes more energy. He's very possessive over her, and everyone who travels with him, except probably Adam. He still doesn't like Adam. Probably due to possessiveness almost as much as Adam being a twat in the end.