I have been using a camelbak vest for 3 seasons now. It is absolutely amazing. So good that I have bought one for my dad, one for my brother, one for my sister in law, one for my girlfriend and a backup one for me (in case they discontinue them).
You can tighten it around the waste and chest so it doesn't wear on your shoulders. I exclusively hunt pheasants and even with the hydration bladder full and three birds in the trunk, my shoulders hold up well.
http://www.amazon.com/dp/B0019D7HT4/...SIN=B0019D7HT4