Or you can pay for "up front" where you get both for a lower price that each separately.

My question is whether this allows you to select a "non-upfront" seat and still keep the large bag. When I booked it, I assumed I could give up that seat but still keep my large bag but when I try to select it online, It seems like the large bag goes away. However it is unclear if this is an artifact of the website or if I'd really lose my large bag.