My mutt does his bit, using a Ruffwear Palisades pack.
Pro: Good bit of kit which comes in 3 sizes, with 2 x 1L bladders for his water. Saddle bags are detachable leaving an excellent harness. Useful handle to help dogs over obstacles - try getting 75lbs of Lab over a stile!
Con: Horribly expensive - look out for sales, there's a new version out so someone may have a few older one left.
Note: A certain pet superstore do a copy much cheaper but they take the view that one-size fits all...wrong and build quality is poor