I have one, but I still take my fanny pack or backpack depending on the time of year. I nthe hotter months, I just wear Under Armour and my vest. All I keep in the vest is the things you need quick or often access to. Everything else stays in the fanny pack, otherwidse the vest gets so heavy it's uncomfortable to wear. Usualy the only somewhat bulky thing I have in my fanny pack is a Gore Tex packable rain suit and of course TP.

In the colder months I usually take a backpack because I will have extra clothes that I take with me in case I need to add a layer in addition to all of my normal stuff and a fany pack is usually too small.