It took me far too long to understand the wtf-ness of this.
In Finnish, 'Jussi' (the Finnish 'J' is similar to 'Y' in English) is a common men's name. Think John or similar. It carries some connotations from classic literature to peasants, hard work, and sisu.
And "pussi" simply means a bag, specifically a simple one usually made out of paper or plastic.
The branding is supposed to invoke an idea of breakfast buns that are traditional, simple, and full of energy to carry you through your day.
Most reindeer live North of the Arctic Circle, where the sun does not rise above the horizon in winter months. I suspect most summer days are brighter than the few hours of twilight the reideer get in December.