System case when empty makes a decent beverage chest.
As to what to take along, as little as you can get by with. Make sure that you have a decent packing system so the stuff stays put. Helen 2 wheels website has some good tips, even if you don't use her stuff
Mosquito repellent is a must, it comes in compact wipes now which is convenient.
Make sure you have a thermorest and get the lightest sleeping bags you can find for the temperatures you think you will encounter. Get a light compact tent but make sure it is big enough for both of you. 2 doors is nice so you don't have to crawl over each other, a vestibule is nice for gear without intruding in the living space. Practice setting it up, tearing down and packing it.
The bike will handle much differently with passenger and camping gear. Don't try to be canyon racer with all the stuff on back.
Take it easy, have fun and enjoy it.