"20/20" SORTS FACT FROM FICTION ON "SUMMER: MYTHS, LIES AND DOWNRIGHT STUPIDITY," AIRING FRIDAY, JULY 4 ON ABC

Can you outsmart gas prices with gas-saving devices or book your wedding a year in advance based on a long-range weather forecast? To mark the July 4th weekend, "20/20" examines common summer myths and misconceptions, including on swimming, sunscreen, lightning and travel. "Summer: Myths, Lies and Downright Stupidity" airs on "20/20," FRIDAY, JULY 4 (10:00-11:00 p.m., ET) on the ABC Television Network. Myths include:

* Gas gadgets: Gas gadgets that claim to save money are flooding the market. But do they really work? John Stossel reports.

* Running on empty: Even when your cars gas gauge reads "empty," there is still more gas left in the tank. Is that a myth or does empty mean empty? John Stossel reports.

* Airline tickets: When it comes to buying tickets and the internet, are coach fares always cheaper than first class? Bill Ritter reports.

* Weather forecasting: Weather predictions translate to big business, but how accurate are they? Sam Champion reports.

* Lightning: Can lightning bring down an airplane? Elizabeth Vargas reports.

* Swimming: Is it dangerous to swim immediately after eating? Dr. Tim Johnson reports.

* Sunscreen: A high SPF gives you full sun protection. True or false? Lynn Sherr reports.

* Vitamins: Do healthy people really need to take vitamin pills to stay healthy? Dr. Tim Johnson sorts out fact from fiction.

Several of these myths are rebroadcasts.

"20/20" is anchored by Elizabeth Vargas and John Stossel. David Sloan is executive producer.