Texas
The state of Kentucky has the longest border, being north of Tennessee, which is much longer east-to-west than north-to-south.
The state with the longest east-west distance in the contiguous United States is California. It covers a vast area from the Pacific Ocean to the Nevada border, making it the longest state to traverse.
In the west, the state of Montana has the longest linear border with Canada. In the east, the state of Michigan has the longest border, including the Great Lakes.
I am assuming by east to west coast you mean the Contiguous US, or the Lower 48. In which case Texas would be the largest state.
Minnesota is approximately 400 miles from east to west.
Africa is the continent that stretches the longest from east to west, spanning approximately 4,600 miles (7,400 kilometers) from its easternmost point in Somalia to its westernmost point in Senegal.
Mexico has the longest east-west coast in Middle America, spanning approximately 2,200 miles along the Pacific Ocean.
Hawaii is the widest state east to west.
Interstates I - 10 (the longest), I-40 and I-80 run east -west across the US.
The State To the west of Colorado is Utah. The state to the east of Nevada is also Utah.
Africa is the continent that stretches the longest from east to west, spanning approximately 7,500 miles (12,000 kilometers) from its easternmost point in Somalia to its westernmost point in Senegal.