The main reason a country would want a sufficiently long line of succession is to avoid becoming extinct. So, from that perspective it doesn't necessarily require each one of those in line to also carry out royal duties as the number of duties to be carried out is limited.
Princess Christina hasn't been in the line of succession, but she has still done a lot of duties which a person who is in the line of succession (or his/her spouse) could very well have done:
- Christina was the Honorary Chairman of the Heart-Lung Foundation 1971-2014, in May 2014 Daniel started as the Honorary Chairman
- Christina was the Honorary Chairperson of Sophiahemmet 1972-2015, in the beginning of 2016 king Carl Gustaf decided that Sofia replaced Christina
- Christina is the Chairperson of the Board of Confidencen Ulriksdal Palace Theatre and the Honorary Chairperson of Confidencen Rediviva
- Christina is the Honorary Chairman of Crown Princess Margareta Foundation for the Visually Handicapped
- Christina is the Honorary Chairperson of Solstickan Foundation and has delivered Solstickepriset every year.
- Christina is the Honorary Chairman of SWEA (Swedish Women's Educational Association) International
- Christina is the Honorary Chairman of the Board of Kultur & Näringsliv
- Christina was active in Red Cross for many years. She started as a volunteer in 1973, acting as an ambassador for the Red Cross' humanitarian values and the international human rights. Christina was also active in the work for a total ban on landmines. In 1986 she was elected into the Swedish Red Cross' board, in 1993 she was elected as chairman, she was the Chairman of the Swedish Red Cross until 2002. In 1995-2003, she was also an elected member of the International Red Cross' Permanent Commission. Christina received Henry Dunant medal for her service in Red Cross.
- Christina is very much involved in the work of the Royal College of Music and has delivered the Jan Wallander Prize during many years
- Christina was the chairman of Karolinska Institute's 200-year campaign "Breakthrough for Life".
- Christina has been very active at The Friends of the Nationalmuseum, now her son Oscar is a member of the Board.
- Christina has delivered the Carina Ari Medal and scholarships in many years. The Carina Ari Memorial foundation's purpose is to develop and support Swedish dance.
- Christina is the patron of Time to Act -campaign, UNHCR's global fundraising campaign to provide Syrian refugee children the opportunity to go to school.
- Christina has in many years delivered the scholarships from King Gustaf V and Queen Victoria's Foundation of Freemasons.
- Christina is the patron of Sweden-Japan Society
These are only part of princess Christina's duties, and during the years she has done many work events which the members of the Royal family also do (for instance delivered the Royal Patriotic Society Medals and Micael Bindefeld Foundation's scholarship), if the members of the royal family have been busy elsewhere.
And since Christina now retires from her duties, at least part of these are that kind of duties, which a member of the royal family should do. So there would be a lot to do for instance for Sofia and Madeleine.