Jars beat bags every time. That 'shrinking trash and spending' line hits home. Started doing the jar thing last year. My grocery bills dropped like a rock. Also makes you realize how much crap you don't need. Forced me to meal plan, which cut impulse buys.
Try storing a five-pound bag of rice in a jar sometime. You'll run out of shelf space before you run out of groceries. The jar method works best for dry goods, not bulk purchases.