As mentioned by a few others, everyone is different because different things work for different people.
My set-up this year will look like this:
Tailfin Aeropack: Tent, poles, microfibre towel. I'll also store some food items in it. It technically can fit a lot more, but I have a dropper post, so want to be able to use it when needed. Rain jacket strapped to the top.
2 x 10 litre mini panniers: Sleeping bag, little inflatable pillow, base layers/shirts on one side, sleeping mat, cooking kit, and first aid kit on the other.
Frame bag: 1.5 litre hydration bladder if there will be lots of re-supply points, some food, spare tubes, and water filter. If there aren't many re-supply points- 3 litre hydration bladder, spare tubes and water filter.
Tailfin downtube bag: tools and spares.
Tailfin top-tube bag: Snacks and phone
Bar bag: rest of my clothes, including sleep/camp clothes and electronics.
When I go with my son on our trip, it will look broadly similar except I'll swap out the 10 litre mini panniers for 22 litre panniers
One side will have all of my kit from both my 10 litre panniers, the other side will have his sleeping mat and bag, and some of his clothes.
His trailer (he'll only be 2.5 years old, so he gets to travel in style) will have toys and snacks with him in the front, and nappies (diapers for the Americans) if he isn't potty trained by then, individually packed toddler milk, and probably a few extra changes of clothes.
Here's some photos of last year's set-up with the 5 litre panniers instead of 10
