Where does the comma go when using the word or in a sentence?

There typically is not a comma when using the Word or in a sentence:

• You could have toast or cereal for breakfast.
• The reason someone gambles is either for excitement or for money.

If you want to indicate a pause between the options, you would include a comma before the or:

• "we could go to the park, or if you'd prefer we could go to the beach."