Pepsi Natural in glass bottles
Throwback is just the normal Pepsi recipe actually using sugar instead of the HFCS that it would normally use. Limited time item.
Natural is a different recipe altogether, reminiscent of Pepsi, of course, but it's not trying to be identical. It, too, uses sugar, but the label lists things like kola nut extract and other more precise ingredients as opposed to the typical sugar water. It's also a lot more expensive; Throwback was sold at the regular price of other Pepsi products.
I've gotten my fill of both, at least for a while. Natural was interesting a couple of times, but not enough to buy regularly. Maybe once in a while. Throwback was great a few times recently, but the last time I tasted it I found myself thinking "eh, it's okay, but I'm not going to miss it that much when it's gone". I have decidedly kicked my cola habit, it seems. I even broke down and had a Diet Pepsi recently, which I drank regularly for years. It really didn't do much for me anymore. Wow.