I always take 2 garbage bags and pack my cycling clothes in 1 bag and the off-bike clothes in the other. Then I stuff the garbage bags in whatever pannier they fit.
This provides an extra water defence and is also very convenient for accessing the clothes - you just pull the garbage bag out of the pannier.
This provides an extra water defence and is also very convenient for accessing the clothes - you just pull the garbage bag out of the pannier.