When I go with just DD8 we bring one of those lightweight drawstring backpacks and we take turns carrying it. Usually she gets the first 1/2 of the day, I get the second 1/2... y'know, when it starts getting heavy... and I get to handle it on all rides. I call her my pack horse! She hates it but hey, most of the stuff in there is hers and I have a bad back, so the only other option is to leave it behind.
I honestly don't know what people put in those huge bags I see them schlepping around. With little kids I can understand, but even then I try to pack as light as possible and use the stroller basket. I'm too lazy to carry around all that crap! Give me my BodyGlide, a lipstick, my camera, my meds and some eye drops and I'm good to go.