B and B credit card tour for me:
I have my normal 5 litre rack top bag Vaude Silkroad 5L. This contains what I normally carry on a day ride being, waterproof, 2 tubes, levers, multi tool, sunglasses and sunscreen.
For the tour I add 1 ortlieb front pannier which I think is 12L (on rear rack)
I pack in the pannier the following:
Spare pair of bibs and jersey
Lightweight trousers and tee shirt for evening plus very lightweight shoes
Toiletries, toothbrush, mini toothpaste, plastic BIC razor, very small small aerosol deodorant that I have mostly used to reduce weight
2 charging cables (phone and GPS)
Lightweight plug with two USB charging points
Spare pair of socks and pants
Possibly lightweight fleece for evening but can use waterproof and leave this out