Grow your own
When I send you your copy of the hardback, I will enclose a photo of a plant from my own invisible allotment – and, free of charge, a part of that plant to grow in yours. Exactly what will depend on what I've got available and what time of year it is, but it'll be seeds, a tuber, a cutting, or some other form of propagation material of something interesting and edible. I’ll email you first to make sure it’s something you actually want! (Sorry, but this offer is only available within the UK).
Plus everything in the Collectable level