I have a small MEC rock climbing bag that has a pocket that will hold a 2 litre bladder (I use a 1.5) and I prefer the Source bladders as their large opening lets you add ice, they are very sturdy, and have treated me well for the past 5-6years.

When it gets really hot, and we get as hot as we get cold, I find that I drink more when I have my hydration bag and often take it on walks and errands as well as bicycle rides... my daughters won't leave home without their hydro bags in the summer and use the same bag as I do.

They will empty a 1.5 litre bladder in an afternoon of riding and I know that they won't be dehydrated after playing in the sun.