react on the spot with your previously thought out response to survive. As though it were actually happening Correct. This is why people train for specific scenarios, over and over again.
In 1940, German forces overran the impregnable Belgian border forts. The Germans did not have superior equipment. MOreover, the Belgians knew that they would eventually attack. The Germans came up with a solution and trained over and over to execute the ingenious plan. Artillery shelling would create craters. Ground troops practiced immediately occuping and fighting from shell craters. A number of casualties in practice. Victory was not through landing pararoops on top of the Belgian forts.
When bugging out is not an option - think of another, in advance.