Folding Snorkel, XS Scuba
 
Snorkels are great for snorkeling. However, lots of ppe feel they are not so great for scuba diving.
 
If you are the kind of person who likes to "have" a snorkel, but not wear one until you need it, a folding snorkel is a great alternative. This one folks neatly into your pocket. 
 
Most of our dive leaders (including me) wear one, and all of our rental BCs have a pocket containing one of these folding snorkels.