This depends on personal choice, which one you are used to, different times are different. There are more than 30 varieties in 10 categories: among them, there are 20 kinds of agricultural products, including corn, soybeans, wheat, rice, oats, barley, rye, pork bellies, pigs, live cattle, calves, bean flour, soybean oil, cocoa, coffee, cotton, wool, sugar, orange rice and rapeseed; 9 kinds of metal products, including gold, silver, copper, aluminum, lead, zinc, nickel, palladium and platinum; 5 kinds of chemical products, including crude oil, heating oil, unleaded gasoline, propane and natural rubber; There are 1 forest products, wood; There are three kinds of financial products: interest rate, foreign exchange and stock price index. You can choose.