Jackie Morris (Artist) has posted a blog asking the question above - What is in the Bottle?
Here is a link to her blog post ... why don't you have a go. There is only a couple of days left, so you'll need to be quick.
I think the bottle holds the spirit of adventure given to Jackie by all the animals she has drawn and painted over the years. It gives Jackie her own sense of adventure as she writes and paints the next story that has come to her in her dreams.