A product that is bought regularly by consumers that is almost a necessity is gasoline. Most consumers require a vehicle to get to important everyday events (work, school, shopping) but also use for leisure, so there will always be a demand. If the price of gas goes up, then demand will go down, shifting the demand curve left. If the price of gas goes down, then demand will go up shifting the demand curve right. The price of the product is inversely proportional to the demand. However, a change of income is a major factor affecting demand. Increased income would shift the demand curve to the right (higher demand). 

Find alternative means of traveling (like carpooling, public transportation, or walking - these are substitutes) to everyday events and may altogether eliminate leisure trips if the price of gas rises too much.