There is something to be said for acclimatization. Once you do a few (or more) rides in the rain, then it doesn't really bother you so much. Choose a few clothes to keep warm if that's an issue. I've only had / have issues when the weather gets very chilly - like on descent from mountain in less than 20c weather. Then, I prefer to have 100% blocking material like plastic. For the inside - I still prefer a few sheets of newspaper which both absorbs moisture and acts as thermal barrier. And - when you're done with the descent - just toss it. Base layer is important. Personally I prefer wicking type, thin wool or raw silk. I hate cotton base layers. They get wet, freeze, stay sodden without doing anything useful IMO.
My highest recommendation for 'long ride', brevet , touring -
Silk Base Layer - you can't go wrong with silk. It's comfy, doesn't stink, stays pretty light when wet and has decent wicking.
Merino Wool Jersey - hands down Merino Jerseys beat anything. Hot, Cold, Wet, Dry. You name it. You can always wear it.
Rain Shell - something with a hood. Anything 100% rain proof with a hood from cheap, conbini jacket to higher end. Unless the weather is really cold - then you'll want something with more insulation as well.
Wool Socks - period. Ride them wet or dry and they are fine.
Embrocation / Sealer - you can also treat your skin against inclement weather by just using some embrocation. My favorite rides in the rainy season are just normal wool Jersey / Bibshort and then use beeswax-base embrocation on legs and arms. After 5min in the rain, totally soaked, but don't even notice it.