My daypack for hiking always has a first aid kit, snacks, and water, bug nets, hats, sunblock, bug spray, or anything else that the season brings.
1 easy-access location to stuff things in that doesn’t have to be contained in a zipped.
They aren’t designed to hold a lot of weight so extra straps aren’t normally needed.
They aren’t designed to hold weight like bigger bags are, but they do keep it closer to my body, allowing for easy movability.