Okinawa Bus - Naha Airport to Nago

I'm going to be travelling up and down Okinawa from Naha to Nago and was wondering if I need to book in advance for the Route 111 bus or if I can just buy a ticket on the day?

Will I be able to take a large backpack on it ok?

No booking bus, also 117 bus goes to.
(4 bus companies shared, same fare)
http://www.city.nago.okinawa.jp/4/3894.html
http://toyobus.jp/unchin_hyo.php?NUM=111

Use trunk room.
http://blog.worldcycle.co.jp/wp-content/uploads/2013/04/002.jpg

This is a bit old, this is "Okinawa bus".
https://youtu.be/Eq0esmi1d-Q
Other company ones, "Naha bus", "Toyo bus" and "Ryukyu bus kotsu".
http://file.mrjohso5003.blog.shinobi.jp/209.JPG
http://img-cdn.jg.jugem.jp/533/3152054/20170517_2130442.jpg
http://tabinori.net/Highwaybus/photo/okinawa/P1820777.jpg

Thank you!