I have the H.A.W.G. (916 cu. in. of cargo room) and the BFM (2550 cu. in. of cargo room, as far as I am aware, the biggest one they make) and use both almost daily. Different applications, the H.A.W.G. I carry all day at work with water, a rainsuit and miscellaneous things I might need during the day. The BFM is my general purpose, go everywhere, bag. I'm of the opinion that it's better to err on the side of too big rather than too small and wind up in situations where you have to tie stuff on the outside of your pack. Besides, all the CamelBaks I've seen have cinch straps so that you can compress it down, to some degree, if you don't fill it up.
I'm hesitant to recommend a specific model because because Camelbak makes so many different ones and because there are so many other manufacturers in that market these days, except to say that the M.U.L.E. might be too small for what you described.
But that being said, I typically don't carry anything on my back when I'm riding. The BFM usually rides in my Burley Flatbed Trailer along with whatever else I might be carrying or whatever I find on the roadside that I want to keep.