This is a two-part suggestion, but both are part of the same general idea.
1.) Allow the player to give specific items to dwarves. This would boost happiness. The side effects of this would include a use for trader crap that isn't trading and a use, period, for artifact mugs and bracelets. It would also allow Toady One to add in some fairly common unhappiness-generating events without severely threatening all forts with tantrum spirals. I believe I have made this suggestion elsewhere, so I won't go into it in much detail--not that it needs much more.
2.) Immigrants (and probably the Starting Seven) would come with some items--a container, a knife (used for protection, eating, and a few other things in the medieval world), mugs, toys (if children), and so forth. They would also probably have coins; this may suggest that clothes would need to gain "pockets," but that is not necessary. A family (or dwarf, if s/he does not migrate in with any family members) would have a semi-random "wealth level" that determines how much stuff the dwarves in the family have. The wealth level would probably also affect pets that the migrants migrate in with.
These suggestions, or one of them, would add a bit of verisimilitude to DF, and would help pre-find a few bugs involving the economy that involve items. They would also encourage bedrooms that are more than a bed, and might add a bit of wealth to struggling forts. One can imagine a group of dwarves taking everything migrants bring, or one that allows migrants to have all of their possessions buried with them. New management might cause items to be removed from the grave, causing unhappy thoughts and likely releasing a burst of miasma that was trapped in the coffin. It would probably be a good idea to let the player choose if his/her fort took all non-clothes from migrants, let them keep their possessions until death, or have said possessions buried with the dwarf and/or passed down to the dwarf's family members. Dwarves might give each other gifts on their birthdays or on procedurally-generated holidays, although these should probably be represented solely by an exchange of ownership. It would probably help the whole "Dwarves only own one set of clothes and never change" "problem."
That's about all I can think of right now. I'd like to hear your thoughts, as long as they aren't "Please organize your ideas better."