Poor soul - there are so many of these bugs about just now. The recommended rehydration solution in the absence of the real thing is watered down lemonade - the water kills the fizz but leaves a pleasant lemony flavoured sugar water which should give him fluids and some energy from the sugar. You can try and tempt him with some favourites, what about custard or my son's favourite when he is unwell is instant mash potato. Another snack that goes down well, is a little bowl of dry cheerios to snack on or a packet of plain crisps. I wouldn't worry too much, it wont do him any harn to go without for a couple of days - he will know best whether he feels like eating or not and he feels like something unhealthy, you can worry about having a healthy diet when he is feeling better!