For smartphones, cameras, etc. I'd go ahead and upgrade to one that's water resistant enough to handle the rain. Though there are plenty of other flaws to my Kyocera Hydro Icon, I am satisfied with its water resistance after several 30-40 minute commutes in pouring rain with it in the handlebar holder.

For dirty/wet clothes, buy a few rolls of poop bags from the pet aisle. Dollar Tree has them in, IIRC, 4 rolls of 20 each for $1. A roll of 20 is about as long as a 35mm film canister but smaller diameter. Put your dirty socks, underwear, etc. in those in daily lots, and then in a tougher large trash bag to go in the pannier. That way when you open up the laundry trash bag to put the next day's dirty laundry in, you're not getting a face full of day old crotch sweat scent. They're also just about perfect for camp trash, and available in different colors so you can easily tell which ones to throw away and which to just not tear open until you're standing over a washing machine.