One Day in London: Harrods | Buckingham Palace | Westminster Abbey

(A) Shop at Harrods
Harrods is the ultimate shopping destination. It is rumored to have anything and everyone anyone can ever ask for (this included an elephant at one point in time). Regardless if you're into shopping or not, the interior and exterior architecture is incredible. During the Christmas season, Harrods exterior is outlined in thousands and thousands of lights. Its windows feature the must-have gifts of the season, and make sure you take a picture with the beautifully decorated tree outside.

[credit: Visit London]
The Egyptian escalator banks in the center of the department store is also a must. The Harrods Dodi and Diana memorials can be found at the base of this escalator. For souvenirs, make sure you stop by the Harrods gift shop, where you can pick up tea sets, toys, and accessories with the Harrods bear.
While at Harrods - you simply cannot miss its Food Halls on the ground floor. There's something for everyone within its 4 food halls! Swing by and pick up a few things for a picnic lunch. I highly recommend their pastry selection!
[credit: Drinks Business, Harrods]
(B) Have a picnic at Green Park and watch the changing of the guards at Buckingham Palace
There are multiple ways to "visit" the Buckingham Palace. You can buy tickets and do a tour of the state rooms inside (make sure you buy tickets in advance). The garden is open to walk through at the end of your visit during the summer in the day (evening tours do not include the garden). There's a Garden Café which also provides beautiful views over the Palace lawns. The 16-hectare garden includes the summer house, rose garden, the enormous Waterloo Vase as well as the Palace tennis court. For a more in-depth view of the garden, you can book a Garden Highlights Tour.
[credit: Visit London]
Even if you don't do the full state room tour, make sure you watch the changing of the guard at the front of the Palace. During the Changing the Guard ceremony, also known as ‘Guard Mounting’, one regiment takes over from another. The Queen’s Guard is made up of the St James’s Palace and Buckingham Palace detachments. The New Guard, who during the course of the ceremony become The Queen’s Guard, march to Buckingham Palace from the Wellington Barracks with musical accompaniment. The ceremony takes place, weather permitting, at 11.00 on Monday, Wednesday, Friday, and Sunday and daily in the summer.
Buckingham Palace is located in between Green Park and St. James Park - which means there are plenty of places to picnic and enjoy the goodies you picked up from Harrods. A great spot to picnic at is towards the north end of the park, where you have a view of Buckingham Palace. There are plenty of other scenic spots along the long pond at St. James' Park as well.
[credit: Britain Express, Duke's]