HAH! And that'd fix the contiguous furniture problem too... (pool tables, benches, beds, etc)
Items are actually easy, Grab->grab what? menu, then grab a pointer to the item.
The main problem with furniture is that it can have "contents" but the linkage is only that they're on the same square, so if you drag around a piece of furniture it will either leave its contents behind, or vacuum up everything as it moves over them. I believe pushing furniture around currently does this, but it's awkward enough to do that in practice it's not an issue, if the grab were persistent it might be.
And that's why I made shopping carts vehicles, because they already had their own inventory.