But there are a few small things you can keep handy to improve your experience. My backpack always has the following in it.
- A light rain shell
- Rain pants
- Trash bag
- Quart-sized zip-lock bags
The rain shell came with a stuff sack, so it packs down pretty small. The pants and trash bag get rolled up and bound with a rubber band to keep them tidy and out of the way. If it's raining when it's time to hit the road, I wrap my laptop inside the trash bag. Phone and wallet go into a zip-lock. Anything else that can be damaged by water should be sealed up as well.
Or you could spend a bunch of money on a solidly weatherproof backpack. In some parts of the country that kind of investment makes a lot of sense. But it just doesn't rain that often here.
What to do with the wearables should be obvious enough. I like to put my helmet on over my hood, since it tends to get blown back if I do it the other way around. If you're worried about your feet getting wet, you can either get waterproof shoe covers, or you could put plastic bags over your socks and allow your shoes to get soaked while your feet stay relatively dry (except for some extra sweat).
Another thing to take into consideration when riding in the rain is safety. Puddles can hide road hazards and can sometimes be deeper than they look, so avoid them when possible. And use caution when a fording is necessary.
Lightning is a serious risk, especially if you have to ride through open terrain. So try to choose a route that minimizes the time spent being the tallest thing around, and haul ass through any unavoidable fields. You're not going to outrun lightning, but you can limit the time spent exposed to greater risk of a strike.
Finally, rain inhibits visibility, so make sure you're equipped with appropriate lighting and reflectors if you're going to be riding in traffic.
If you're always prepared for a little stormy weather, you can bike your commute without worrying about gambling with the forecast. The weather is going to happen; just roll with it!