I would move out of my apartment into a house again. I would take my roommates with me, but we would each have our own room.
I would spend one weekend per month, and then one month in the summer, somewhere else. Somewhere pleasant, like Ireland or Mexico City or the Adriatic.
I would always have Oreo cookies in the house, and I would buy high-quality peanut butter, shampoo, and sour cream.
I would decorate my house with vinyl wall stickers and brightly colored paint, matching endtables, fancy ottomans and couches without rips in the fabric.
Bookshelves. The pottery barn kind that's like a wall of cubes, and the kind that's like leany shelves. The house would never be cluttered because there would always be an empty space to put things.
I imagine that if I were immensely rich, I would end up buying many pairs of nice jeans, and many shirts of the same kind in a rainbow of colors. I would always wear the same outfit, in varying hues.
I would buy a puppy. An expensive puppy from the puppy store in the mall, where they're all cute and furry. I would hire someone else to take care of the messes the puppy would inevitably make.