Carol, the difference between "no bag tier" & 1 bag tier is $15. if you take the 1st tier then decide on a bag and enter it when getting boarding pass the charge is $5 more or $20. If it's done at the airport it's more.
We used to travel with carry-on but after discovering JB started checking one bag. But when at their web site I saw no way to choose 1 with no bag and another with 1 bag. Rep said to do that you'd have to make a separate booking for each person.
I chose 2 bookings no bag, knowing if I decide on a bag I'll pay $20 more---since difference in cost would have been $15 per booking ($30) I feel I'll save $10 if I take a bag.
Not sure if will check bag or not since my flight arrives after 4pm. May be easier to grab carry-on meet Leslie and take off. Can't remember wait time for luggage in the past.