Author's notes:
Montgomery was usually not fussy about dates. I've assumed that Jenny is born in about 1922, so most of this story takes place in about 1928. From 1922-1930, Canadian Thanksgiving was celebrated on Armistice Day, November 11.
The Curtiss JN-4 two seat biplane, developed as a trainer in WWI, was one of the most popular aircraft of all time. After the war, hundreds were sold for civilian use, and it became the plane most identified with the barnstormers of the 1920s. Since a Jenny only had a useful load of 500 lbs including pilot and fuel, Shirley would only have been able to carry one passenger at a time, and his cargo was probably limited to important messages, mail, and small items.
I was unable to find any reference to rationing after WWI, so presumably it ended with the end of the war (as opposed to Britain in WWII, where rationing continured into the 1950s).