Warm rain, over 60, I usually just get wet.
A helmet cover is a big plus -- get one that's bright yellow, not black, if you're riding in traffic. Motorists have a harder time seeing in the rain, might as well stay visible.
On my feet, SPD sandals stay much warmer than wet shoes, no mass of wet fabric sucking the heat out of your feet.
Backpack is a
Seattle Sports AquaKnot drybag in bright yellow.
Cool rain, over mid-30s, I wear knee-length rain pants and layer my upper body so I stay warm but damp.
Rainy Day Conspicuity - Rear by
joshua_putnam, on Flickr
Rainy Day Conspicuity - Front by
joshua_putnam, on Flickr
Below mid-30s, I'll add socks, full-length thermal tights, and a rain jacket.