DD went onto Concerta at age 6, when she was DX'd initially - that was all that was on offer to her, no other options for treatment or otherwise learning to manage it.
She was always small for her age, but it did reduce her appetite further and she was on the 4th centile for a long time. She had still been in the habit of a drink of hot milk before bedtime, so I kept that up as a way to make sure she had lots of calories getting into her (in fact, I went from low fat to full fat milk, and we did lots of hot chocolate topped with squirty cream nights instead of plain milk - partly to encourage her to have it, partly to get calories into her, and partly to have warm milky drinks before bed to promote sleep).
She was not a sandwich person in school, so I used to cook pasta and put in a food flask with a handful of grated cheese or of pesto for her lunch a lot.
Things like extra cheese, plenty of hidden veg including beans and pulses in meals, accepting her foibles about food and making a dinner she would eat so that she actually ate rather than making a stand that she had to eat what was cooked....part of it related to having very little control over certain things and food was something she could control so better for her to actually eat (I could always freeze leftovers of her uneaten planned meal for DH or I to have another night instead) and have less stress etc.
Things like having hot food (eggs some mornings, sausages another, pancakes were a favourite etc) for breakfasts to fill her up before the meds started working.
The big milky drink and something to eat going to bed.
Having things she might snack on available when she came in from school, or in the car (and aiming to have relatively healthy options - not just sweets/crisps) - raisins, carrot sticks, pepper sticks, breadsticks/crackers.
Getting enough fat into her - full fat milk, extra butter in mashed potatoes, lots of cheese.
And accepting she has an issue with the texture of red meat, so going for lots of chicken and fish that she would eat. And mince meat sauces were ok sometimes.
As it happens, she learned enough through courses I did, a helpful SN teacher for resource in 4th and 5th classes and a very understanding class teacher in 5th class in particular, to come off concerta in 5th class. She still takes melatonin for sleep even today. But she had learned enough coping skills to manage without meds, and it allowed parts of her personality to come through that were masked by the meds.
They were really important when she was younger and really couldn't cope with busy classroom and expectations.
We still have plenty of "fun" times at home, but she manages in school etc well now generally, and does a LOT of sport to take the hyperness out. She still has issues with food (partly control, partly a teenage thing, partly a serious sportsperson thing....) but has generally kept to the relatively healthy habits she always had as sugar is a really bad thing in her mind (but you can get so many sugar free things now....who knew!).