I'm not really confident about what qualifies as "common food" or "typical western diet", nor the accuracy of the following sources, but I feel like if someone's going to answer OP, they should have something to back it up.

Onions - 5,500 years ago
http://www.vegetablefacts.net/vegetable-history/history-of-onions/

There are two schools of thoughts regarding the home of onion cultivation, and both look at the period 5,500 years ago in Asia. Some scientists believe that onion was first domesticated in central Asia and others in Middle East by Babylonian culture in Iran and West Pakistan

Sugar - 6,000 years ago
https://en.wikipedia.org/wiki/History_of_sugar

The extraction of sugar cane juice from the sugarcane plant, and the subsequent domestication of the plant in tropical India and Southeast Asia sometime around 4,000 BC.

Beans - 7,000 years ago
https://cablevey.com/history-of-dried-beans-how-it-all-started/

Examining the origins of the dry bean takes us back to South America. These, serving as a dietary cornerstone, were initially cultivated over 7,000 years ago in the southern regions of Mexico and Peru.

Corn - 10,000 years ago
https://cropcareequipment.com/blog/corn-farming-history/

People have been farming corn, or maize, for thousands of years. Native civilizations in present-day Mexico first domesticated corn around 10,000 years ago.

Potatoes - 13,000 years ago
https://spudsmart.com/domestication-of-the-potato/

Wild potatoes from the (then) humid coastal plains of South America were probably first eaten by people as early as 13,000 years ago.