We gathered our essentials, took off for the great outdoors, and ignored the fact that it was Friday the 13th.

Please telephone me if you cannot send the information promptly, or if you have any questions.

The first sentence correctly uses a comma between all items in a series. In the second sentence, the comma before or is incorrect because it separates two subordinate clauses, not two independent clauses.

For more help, see section 32.