No there never is, there will be a lunch.
Before Queen Sonja the last woman to attend the opening was Queen Maud who attended 5 times. The Crown Princess never attends for some reason, maybe because they just have three chairs
Stortinget has a story about the chairs used, the Throne is belived to be from 1847, made by an artis called Wilhelm Heinrich Hoffmann in Stockholm. Some historians thinks it is originally made for the coronation of Oscar I.
the two other chairs are stylistically so different that they are not belived to be from the same time as the throne. They are in empire style and belived to be from the early 1800.
Queen Maud was the first woman to sit on the podium next to the King, before that the Queen, the underaged Princes and female members of the court sat in a lodge where the diplomats sit today. Whils the Heir and Princes of age accompanied the King, the chairs was therefor called "the Prince chairs"
For the swearing of the oath in 1905 they had no available chair for the Queen so they had to borrow one from the National theatre

in 1906 one of the "Prince chairs" was turned into a "Queen Chair" Both Prince chairs got the Norwegian Lion carved in and and the new Queen chair got a closed coronet to symbolise the Queen, whilst the Prince chair has an open crown.
The Queen chair was always placed in Stortinge even if Queen Maud did not attend, the last time she attended was in 1922. The Queen chair was the brought out again 69 years later for the swearing of the oath of King Harald in 1991 when the new Queen Sonja accompanied him for the first time.
www.stortinget.no > tronstol
Picture from the opening of Stortinget including the chairs
http://www.kongehuset.no/aim/kongehuset/20/89/storage/file.image.jpg/Scale?geometry=766>x241>
about the opening in english
kongehuset.no - Opening of the Storting
Here you can see the Queen Crwon over Sonjas monogram
kongehuset.no - Hennes Majestet Dronningen
and the crown of the Heir
kongehuset.no - H.K.H. Kronprinsen
which is the same as Ingrid has
kongehuset.no - H.K.H. Prinsessen
whilst Sverre Magnus has an completely open Crown without the pillow inside or what you want to call it
kongehuset.no - Prins Sverre Magnus
Queen Sonja usually wears suits in black and red, though I belive she wore black an purpel once.