"Show an understanding of the importance of a sensible and appropriate diet and the need for sufficient sleep"
The Scouts will be given a range of ready to eat food samples that cover all of the good and 'less good' foods, from the samples provided they need to prepare a balanced menu for 2 days worth of meals.
Once they have succeeded in creating a balanced menu, they can eat it !!
Variety of ready to eat food samples
The scouts should work in patrols, they will need to wash their hands before starting, an ideal opportunity for a reminder re food hygiene.
Consider food allergies before commencing the activity.
The food samples need to be scaled down to bite-size, not full portions, to create the balanced menu there need to be smaller quantities of those items you would expect there to be less of, such as high fat, high sugar items, and more fruit/vegetables/fibre etc.
The patrols should end up with a plate/bowl for each meal, 3 for each day of the 2 day menu.
Once the menus have been laid out on their tables work around the room asking the patrols to explain their menu choices and to check they've got it right (there are probably any number of different ways of reaching the right answer, provided the final 'balance' is correct.
Needless to say when it comes to eating the food the scouts will inevitably want to eat only the high-fat, high sugar items, but they are to be told those items can ONLY be eaten once the rest of the 'balanced diet' has been consumed by the patrol, hence achieving the desired balance !! (leaders feel free to engage in maniacal laughter when explaining this rule)
There is a sleep element to this part of the Fitness Challenge, this can be covered after they've eaten by a Q&A, perhaps establishing how many hours a night each scout sleeps, and then a discussion about the reasons for getting the right amount of sleep.