For me it's generally one large pack (30-45l) and a small sling bag (maybe 10l.) I generally also carry a very small packable backpack for beach trips, day trips etc. And occasionally for food transport between hostels.
I try not to get too hung up on definitions about that sort of thing since it tends to lead to a lot of silly arguments and gatekeeping(see UL type forums) the carryon only thing is mostly the draw for me anyway. I typically take two bags, a Porter 46 and a small backpack that typically is a personal item/daypack/hiking bag. Usually the small backpack would fit inside the porter, but not always depending on what all is going.
@hsl I never heard about this term until now, but I can give an insight on what do I usually take in my backpack whenever I leave the house for a longer trip:
a compact umbrella
some tissues
a powerbank for my phone (despite nowadays my phone battery lasting more than a day and being replaceable)
a pen
a 0,75-1l bottle of water
All these usually fit in a small backpack like mine just right.