Bike stuff won't rust if you dry it off after you ride and keep it lubed.

The most essential gear for wet weather riding (and I've ridden in hard rain from 85º down to 40ºF with some regularity this year) is booties for your shoes (nothing's worse than wet/cold feet) and the right gloves for your hands (except cold hands). I wear booties when it's not raining but the roads are wet. Period.