Soft Mick is a character who lives in small parts of houses inaccessible to others. He can move through cracks and under doors (hence the "soft") pinching things such as socks, teaspoons and all the other stuff that you could have sworn was there a minute ago. So he has a collection of all types of things. If someone has a large amount of something, they can be said to have "More xxxx than Soft Mick"