I also have second and third prizes too, just to make sure everyone receives a treat. Regularly update question cards to ensure they do not lose interest or to make it a little more challenging mark the question marks in different colours and make up sets of cards in the corresponding colours with each colour tackling a different topic e.g. spelling words, maths, science, social studies, etc. Home made word finds are great to get children familiar with those dreadful words like reign which simply cannot be sounded out. My girls love word finds simply for the challenge but some children may need an added incentive, a treat perhaps for finishing the task. Make incorrect statements about a topic which they have been studying and have them pick up on it.
Lollies always work wonders with multiplication and division.
Share the jelly beans out to check their answer. Reward them with a small treat or extra pocket money for each correctly spelt word they find. Recently, I've added to this exercise to make it more challenging and to help them with multiplication skills by marking their work and returning it, asking them to work out how much extra pocket money they have earned if I was to give them six cents per word. I differ the amounts between six and nine cents depending on the difficulty. I always find that incentives work better when the child has some input into what the treat should be.