Sentences which are punctuated correctly are: 
- Darren told me about his travels to different tropical islands: Hawaii, Puerto Rico, and Jamaica. 
-There are several activities to choose from at the resort: snorkeling, swimming, and hiking 
 Punctuation are used to organize a sentence additionally to create more clear sense and stress in a sentence. 
In the above sentences, The punctuation Colon (:) organizes the sentence properly when placed rightly. Colon is used preceding any list, explanation, description or definition. 
 Colon is one of the punctuation which is used to: 
 1. Lay emphasis 
 Example: He loved just one: Bruno, his dog 
 2. To present dialogue ( we write the name of the speaker and then insert colon followed by his/her dialogue.) 
 Example: Rita: How are you? 
 Mary: Fine, and you? 
 3. Clarify composition titles ( to explain parallel ideas colon is used in compositions like lectures or book titles), and 
 Example: Rousseau’s Dog: Two Great Thinkers at War in the Age of Enlightenment 
 4. To introduce text or lists. 
 Example: Three types of Subordinate or Dependent Clauses are: Adjective clause, Adverb clause and Noun clause