There are some really strange superstitions. My sister-in-law for instance will not take off her cardigan or any other clothing and put it the right way round if she has accidently put them on inside out, as she believes it will bring her bad luck. But leaving it on inside out could bring her good luck. It does look like the general opinion for this superstition stems from the fact that someone had worn their clothes inside out and had great luck that day, so a superstition is born.
Keeping your fingers crossed is a worldwide known way of hoping for your own good luck and to show solidarity to others. There are two schools of thought where this is derived from. One is thought to go way back to the middle ages. Before Christianity they would show a cross, which was considered a very powerful symbol, and they believed it would bring spirits to bring them luck and they kept this sign until their wish came true. The other derived from a way to show support to someone. You would cross your index finger over their index finger. They eventually realized that they could do this themselves, by crossing their own two fingers.
Salt has many superstitions. Spilling salt is bad luck. Buddhists believed salt wards off evil spirits and after a funeral they throw salt over their left shoulder. There was a belief that the devil hung around your left shoulder and the salt would ward him off.