I find the perfect “day pack” similar to what is the perfect holster, I’ve tried so many and been disappointed. As mentioned in this thread I prefer a top load pack that will stand and stay open without falling over or crumbling in on itself. Right now I use a GPS pack that was made for a multiple gun range bag/pack it stands without falling over. I also found a stiff cardboard box of the perfect size that fits in the bottom of the pack to help in packing and support of items. It also has upper and lower chest and abdomen straps that help to keep it secure and in place.
Good but still not the perfect pack.