Baby wipes and antibac hand gel.
Loo rolls in sealable bags, (nothing worse than soggy loo roll). Plus packets of hankies when out and about.
Bucket with lid is a great idea for night time peeing, portaloos are bad enough in daylight.
Bum bag for vitals and valubles.
Bottle to fill the night before for morning teeth brushing and face washing, always a big queue at taps in the morning.
Personaly I wouldn't cook on a camping stove, too much hassle and too much to carry.
Thankfully I have the luxury of a power supply and do bacon and tattie scone butties for everyone in the morning.
Make solid arrangements incase of losing each other.
Ensure you know who is with you.
Don't assume the other has the child.
Don't depend on mobile phones for communicating (often no signal or to many phones on the go).
Arrange regular meeting times at set points throughout the day.
Ensure child knows who are safe adults to approach and point out the different uniforms, staff such as litter pickers are often foreign workers with little english and stall workers and promo staff don't have communications with security or police. So point out security/ stewards and perhaps get a wristband with contact details on inside for child.
Sorry I go on a bit, its just I have experienced this.