My "dayhike" kit is identical to my overnight backpack kit. I always hike with my full backpack kit, even when I don't intend to stay overnight. It helps keep me in condition for backpacking (a Colin Fletcher habit that I never tried to break), and it takes all the "gotta get back before dark" pressure away: if it gets dark, I've got my headlamp and, if worse comes to worst, I just make camp. (Of course, I might feel differently if I was carrying more weight.)