I have an outdoor research dry bag/day pack combo that I do sometimes take.

Having said that, my main backpack is frameless ( a granite gear virga) and weighs a bit over a pound. So my daytrips, I often just take my main backpack, crank the straps down to make the body smaller, and take that.. no need to have a seperate daypack.

Even if you aren't using a frameless main pack, there's nothing wrong with carrying your main pack, mostly empty, on dayhikes. Why carry more stuff?