A good or wind shield goes a long way to keeping some of the off your body at speed, and reducing the chill factor in cold weather. Heated grips are also regarded as a must by many in cold climates, regardless of whether its raining or not. If it rains a lot, consider choosing softer compound that will grip on sealed roads better. The general consensus is don’t reduce your air pressures for sealed roads, but drop the air pressures for dirt roads in wet weather.
Most decent luggage options will be waterproof. Even cheap ones throw over bag have a waterproof cover you can drag over when it rains. If you are on a really tight budget, the dry bags available from camping stores work quite well too.