Bike shorts are worn without underwear and must be clean every day. I take 2-3 pairs on tour.
Breathable raingear is essential. A more breathable thin windproof could be just as useful when its not raining or just "soft*". Even expensive goretex gets clammy. I use a simple ultralight polyester windproof pullover.
Gloves are useful when you are riding but essential when you are falling.
Take a selection of short-sleeve and long sleeve jersies with you, they dont need to be cycling specific but it better to avoid cotton and use synthetics.
It can get cool and wet and some form of leg protection may be needed. Use sports leggings/tights, legwarmers or ultralight showerproof over-pants.
* A soft day is one where there is misty rain in the air but its not going anywhere, even down.