@Lizzie Apart from all the obvious things like clean bedding, towels, etc, I make sure that I have fresh flowers in the bedroom and a small bowl of Cadbury's Roses chocolates (I buy these on discount in a big tub). Also, as I mentioned in a post a few weeks ago, I make sure I have enough spare light bulbs for the bedside reading lights, desk lamp etc.
I also provide lots of leaflets about London and local attractions - Windsor Castle, Stonehenge, West End shows etc, which are often for specific time periods, so once a month I go through them and chuck out any that have expired.