> Waterproof bags probably exist, but I can't say I've seen them available, or used, by anyone at all.

What? Almost all non-cheap backpacks are water-proof. Water-proof packs are around everywhere.

Right? I think that I would have to try to find a bike pannier that ISN’T waterproof.

I honestly never owned one in my life, nor I believe I ever seen one. Note that by "waterproof" I mean something I could stuff a laptop into and have it survive half an hour of heavy rain in it. Not something that will resist a small drizzle for few minutes before its inside surfaces start to get wet.

Where I live a pair of detachable waterproof (yes, you can literally take a 1 hour shower with them) bike bags is about 30$.

I must live a very peculiar life then. All I need is a backpack and a rain coat, it's been 7 years or so and I haven't experienced anything life changing so far

I get on my bike, go to the store, office, friends, &c. rain, snow, sun, wind, it won't kill you really

Let me guess

No kids?

What you described was my bike centric life as well until it wasn't.

When you have to do school drop-off a couple miles away for middle schoolers, or do that weekly store run for a family, it gets a bit trickier on the bike.

I have kids. They’re sitting happily in the dry under the canopy. It’s great. Wherever I need to drop them off, childcare, sports, friends, I park right in front. Predictable travel times, no stuck in traffic. My long term cycling average speed is on par with the average car speed in Berlin. Sure, on some distances I loose vs. a car, but on others I win, since I can take shortcuts or pass cars stuck in traffic.

Bike packs 100kg of stuff or a large shopping trolley in volume. Works for the weekly shopping without issue.

The only time it sucks is ice on the road. Snow is fine, but ice is not - because bike lanes get treated like third class infrastructure, worse than pavements.

I do the school run (3 hilly miles each way) seven times a week on an e-bike - a Tern GSD. It’s fine. Our kid loves it and so do his friends (we share lifts). We do have a car but I haven’t driven it since August.

Waterproof bags have existed for centuries - waxed fabrics, well-treated leathers, and I'm sure plenty of more modern textiles. Or just put a plastic/metal box on the side/back of your bike and use it exactly like you do the trunk in your plastic/metal box of a car.

Waterproof bike panniers are pretty standard.

Waterproof bags or backpacks are absolutely common for electronics. Alternatively, you can buy simple rain covers for backpacks. Bike panniers are at least somewhat water resistant unless you opt for the cheapest. That’s really one of the easiest things to solve.