Hi pinkEmily,
Basically I would cut out all unhealthy fattening treats (nuts, yoghurt drops, those honey sticks) and just stick to his plain regular food. You can also still give vegetables, but also keep an eye on his 'hoard' you ideally want his stash to be as small as possible, without causing him stress, so that he is eating a balanced diet, but not having food to gorge on...
...ahhh if only someone would take me in hand too - empty my fridge and put healthy meals in front of me 3 times a day!