Succession

This will probably put me on every terrorist watch list, but I just wanted to know the protocol when Queen Elizabeth II dies.

First, British law states that the throne is never left vacant, and the new monarch succeeds the old immediately.  (Hence, "the king is dead, long live the king!")

The line of succession is generally determined by primogeniture, which states that children are given precedence over siblings, males are given preference over females, and then by age.  Thus, if Prince Charles should die first, his son Prince William would be the heir apparent, not his brother, Andrew.

(When William and Kate married, Parliament talked of changing this, so if William's first child were a girl she would not be supplanted later on.  However, as the Queen is the head of 44 Commonwealth countries, they would all have to change the law to accept this, and they feared this would re-ignite the debate in Australia over abolishing the monarchy altogether, so they have shelved it again.)

However, Parliament has declared it can decide the successor, and has overruled primogeniture on several occasions.

Second, the new sovereign decides his "regnal name." Generally in the UK, monarchs use their own name, although Queen Victoria took her second name ("Alexandrina Victoria") as did her son (Prince Albert Edward became King Edward VII) and great-grandson (Prince Albert Frederick Arthur George became King George VI.)

When Princess Elizabeth Alexandra Mary decided to keep the name Elizabeth, this caused two problems.  First, all references to the original Queen Elizabeth (1533-1603) had to be changed to Queen Elizabeth I.  And second, in Scotland -- which was not part of the United Kingdom in 1603 -- she was the first Queen Elizabeth!  Many post boxes -- which normally bear her royal cypher "EIIR," for Elizabeth II Regina -- were vandalized to remove the "II" so they now bear the Crown of Scotland alone.

Finally, a proclamation of accession is publicly announced in all of the Commonwealth countries.  Of course, the UK has all sorts of pomp and circumstance around this, but the important thing is that it is made known to the public, which was an important consideration in the pre-CNN era! (You can see the Pathe newsreel of George VI here.)

And that's it. The coronation is usually delayed for a period of mourning, as well as to give time for all of the preparations.  King Edward VIII reigned for 326 days and was never crowned.  Queen Elizabeth II ascended the throne February 6, 1952, but the coronation did not occur until June 2, 1953 -- 16 months later.  In any case, it is a ceremony only, and has no legal merit.

When Queen Elizabeth II dies, I'm sure we won't see the sort of histrionics surrounding previous successions:
- William the Conqueror nominated his second son as successor.  When William II died, his brothers fought for the crown, with the third son prevailing, becoming Henry I.
- Henry I named his daughter Matilda as successor, but when he died his nephew Stephen took the throne, starting another war.  As part of the settlement, he named Matilda's son, Henry II, as his successor, thus restoring the original bloodline.
- Henry II (best known as Peter O'Toole in Becket and The Lion in Winter) had five sons, all fighting for succession.  At the age of 17, and with his older brother Geoffrey, Richard the Lionhearted tried to seize the throne from his father, but failed.  He later inherited it, but while he was fighting in the Crusades, his younger brother John tried to seize the throne, and failed.  (You can read Robin Hood for more.)  Richard designated his nephew as heir, but when he died John finally seized the thrown.
- It then passed from father to son for three generations, to Edward III.  Edward III had three sons: Edward, Lionel, and John.  Prince Edward died before his father, and so, according to primogeniture, the crown passed to his son, Richard II.  When Richard II died without issue, the crown should have gone to Lionel's son, Roger.  However, John's son, Henry, seized the throne instead, become Henry IV and igniting the Wars of the Roses between the houses of York and Lancaster.
- Henry VI of Lancaster was deposed by Edward IV of York.  Henry and his son were murdered, and Edward's son was proclaimed King Edward V.  However, his uncle locked him and his brother in the Tower of London (the princes in the tower), and usurped the Throne to become Richard III.  He was later deposed by Henry Tudor of Lancaster, who became Henry VII.
- His son, Henry VIII, defined his own line of ascension, beginning with his third son -- and only male -- Edward VI, followed by his elder sisters, Mary and Elizabeth.  Edward, however, named Lady Jane Grey as his successor, but she only reigned for nine days before Mary deposed her. 
- Elizabeth (now Elizabeth I) refused to name an heir.  On her death, James VI of Scotland -- her first cousin twice removed -- took the throne, thus uniting England and Scotland for the first time.  (He was known as James VI in Scotland, but James I in England, and is often abbrieviated as "John I and VI".)
- His son, Charles I, was beheaded by Parliament, and the monarchy was abolished.  However, rather than introducing a true republic with an elected head of state, Parliament declared Oliver Cromwell as "Lord Protector" for life, and gave him the right to name his successor.  In effect, he was the king without the title.
- He named his son, Richard Cromwell, but when he turned out to be ineffective, Parliament reinstated the monarchy and offered the throne to Charles I's son, Charles II.  Charles II died without issue and the throne passed to his brother, James II (James VII in Scotland), who was a Catholic.  Protestants forced him to abdicate and flee the country in 1688, and Parliament then ignored primogeniture, skipping his Catholic son and offering it to his Protestant daughter and --oddly -- her husband William as a "joint sovereignship." William became William III of England and Ireland, and William II of Scotland.
- Finally, in 1701, Parliament got tired of all of this and passed the Act of Settlement to define the lines of succession, and declared that Princess Anne would be followed by Sophia of Hanover, granddaughter of James I and VI, who was something like 26th in line but the only Protestant.  Parliament also declared it an act of Treason to "endeavour to deprive or hinder any person who shall be the next in succession to the crown."
- Scotland, who was not consulted, passed its own Security Act stating it would select its own heir.  England responded with the Alien Act, threatening to cut off trade with Scotland unless they joined Parliaments.  This lead to the union, in 1707, of the United Kingdom.
- Sophia died before Anne, but her son became George I.  Even though there are more than 5,000 legitimate descendants of Sophia, there have been no major challenges to the throne since. 

During WWI, George V changed the family name to Windsor, to distance himself from the Germans, but the same house has been ruling England for 300 years.  However, Queen Elizabeth II is the 32nd great granddaughter of Alfred the Great, the first effective King of England, who was crowned in 871 A.D.  Check it out.