I carry a waist pack (or bum bag as we Brits call it). In it I kept credential, bank cards and extra cash in a waterproof pouch, camera, tissues, , spending money for the day, painkillers (unused on my recent camino, constantly used on my first!), biro, ear phones, portable external battery charger (great piece of kit), charging leads, a couple of hair bands and clips. My phone lived in my pocket most of the time but there was room for it in the bag. And I also hung from the belt my 750 cl water bottle in an insulated bottle holder.
Keep in mind that when it is hot, condensation will form in the pocket closest to your body. If you have electronic equipment in here it might be best to keep it in a ziplock bag.
I find that I don't feel the weight when carrying it from my waist. When I am day walking at home without a full backpack I prefer to use a waist pack rather than take a day backpack. It holds all I need for myself and my dog and I carry two water bottles hanging from the belt.