A few months ago I brought myself a backpack and it's a Laura Jones Small Quilted Backpack. It's the perfect size for everything I want to carry around on a everyday basis and more. It retails for $50 NZD and I think that's super affordable for the quality of bag you're getting.
I carry the bare basics in my handbag and I try not to hoard receipts and rubbish in my bag. I permanently keep things likes my favourite hand cream which is currently the Essano Nourishing Hand Cream, lip balm, headphones, a face powder, hair tie and all those kinds of bits and pieces.
I also keep my wallet, Kikki K Textured Leather Card Holder, my keys, a water bottle and my phone. I don't carry too much with me which means that my bag stays light but it also leaves room if I need to taking anything specific with me on any given day.