My daypack always contains water, snacks, an insulating layer, and my ditty bag (which includes my first aid and stuff) and silponcho. More or less, once I'm
kind of out there and not likely to see other people I ensure I take enough stuff that I could overnight if I had to in an emergency. From experience, not that comfortably, but also not in danger of death from exposure.

basically the little poncho tarp weight 250 grams, my first aid and emergency supplies weighs 582 grams (typically). Figure on about another pound (500 grams) of jacket and insulating layer (a sweater or light coat). So I'm probably carrying three pounds or so of gear on a dayhike. Maybe a bit more if it's cold and I add another layer, then add a kilo (two pounds) of water and up to a pound of snacks. So my typical dayload is probably about six pounds all in.

In a cinched down main pack that weighs a pound itself, I don't even really notice it.

Of course if your main pack weighs six pounds to begin with (because it has all the bells and whistles to climb everest and have detachable fanny packs and a dedicated espresso maker pocket, well, your load's twice that 12 pounds still ain't bad. (compared to 40 or 50 )

And therein lies part of the challenge, you want a light daypack because your main pack is packzilla. You need packzilla because you have to carry lots of stuff. You carry lots of stuff because you need other stuff.. vicious circle. It's not one to break out of immediately - just one that takes some practice in figuring out how to dual purpose or multi-purpose gear, and figure out what you really need to take versus stuff that's just stuff.