I don't drink nearly as much Coke as I did as a youth, but when I do, I try to buy it in 8oz glass six packs, which are usually tucked in the far corner of the soda aisle.
It's more expensive per fl oz than plastic bottles or cans, though it still works out to just $0.67 per bottle, but there's a huge psychological difference to drinking a Coke from a glass bottle. The product just tastes better. Classy packaging works.
It's also 8 oz rather than the 20 oz of the plastic bottles in the machines, but IMO 20 oz is more soda than I need with one meal. With just 8 oz, you have to savor every sip, and by consuming less sugar, you're setting yourself up for a smaller sugar crash later.