Pureto rico
Panama Canal zone and Alaska.
cuba
cuba
Guam
Yes, there are two separate Islands- and both issued stamps and were/are British protectorates or colonies.
In addition to the State of Hawai'i, the Commonwealth of Puerto Rico is an island, as are the territories of the American Virgin Islands, and protectorates (Guam, Marshall Islands, etc) and millions of other islands.
The islands, formerly Danish possessions, were sold to the USA by Denmark in 1916.
St, Thomas, St. John, and St.Croix
Most of the former colonies and protectorates are either independent or have been made divisions of the country that rules them. French Guiana (Guyane) is still a territory of some sort of France. Hong Kong is still under control of China. Russia rules part of the the Ukraine.
Alaska and the Midway Islands
Because they aren't inhabited (or are very sparely inhabited) In 2009, the US released quarters featuring Washington DC, American Samoa, Guam, the US Virgin Islands, Puerto Rico and the Northern Marinara Islands. The other US protectorates such as Midway Atoll and Baker Island are not inhabited and so they don't have quarters because of their low significance.