I use either the weed sprayer (if we have pets around since they're great for that) or one of those Advanced vinyl bags; although I've busted a few bags they still are the best for heating water. Beat my friends Nemo and the blacked out weed sprayer, but it's kinda to be expected given they have that clear side and can lay flat. Of course if you've got a stove that's a non issue.
I also use the Simple Shower. It's kind of a misnomer, since it's so useful for all kinds of stuff. Like doing dishes especially (different bottle for rinse water and one for bleached water). For cleaning windshields, for drowning fires, for cooling off, etc. It's always laying around in my sink.
For more established campgrounds a LSI/Sceptre can with a hose fitting, hose and regular garden nozzle does the trick. Just kinda heavy so you need something up high for gravity feed unless you pressurize it, which works well too. Nice in that unlike the flaccid bags it's something you're likely to have for water storage. And much cheaper than the fancy bags.