Most of what I carry is quite bulky (jacket, fleece, lunch box, bottles/flasks), the only things that would fit in little pouches would be first aid kit, torch, snacks, microspikes and water filter so I need to use a pack.
If you want to try a modular system you could buy a Molle pack, Amazon and ebay have loads of pouches and means of attaching them if you want to go down that route.