Moving away from throwing money at the problem, my first instincts were to keep the story simple and base it around vocabulary I have already covered. I could review the relevant flashcards at the beginning of the lesson, and then change tack to start the story.
I mentioned in my last post my Thursday K3 class' love of zombies. I have been teaching vocabulary (since the toys topic last month) with an alternative zombie version of the mime or action that goes with the word, so it goes without saying that zombies will be featuring in the story. I don't have a flashcard for zombies as I think that would be a little too scary. I just act as a zombie or get the children to act out being a zombie.
List of past topics and words from which to choose for story (in bold any ones I think promising for a story):
Clothes (dress, skirt, trousers, shorts, tie)
Rooms in a house (living room, dining room, bedroom, kitchen, bathroom)
Things in a house (toilet, bed, TV, computer, wardrobe, toys)
Shapes (circle, square, triangle, rectangle, star)
Vegetables (cauliflower, carrot, cabbage, cucumber, (baby) corn)
Sports (football, basketball, tennis, swimming)
Vehicles (train, plane, bus, bicycle, boat, car)
Adjective (rich, poor, fast, slow)
What's the time, Mr Wolf?
Toys (doll, teddy bear)
Simple Command (make a line, make a circle, hop, jump, hold hands, hold shoulders)
Sign - Symbol (No Smoking, Fire Exit, Pharmacy, Hospital, Rest Room)
Number (Add-minus) (plus, minus, equals, 1-12)