What’s the easiest way to stop WP from ever logging me out

By default, the “Remember Me” checkbox makes you get remembered for 14 days. This is filterable though.

This code will change that value:

add_filter( 'auth_cookie_expiration', 'keep_me_logged_in_for_1_year' );

function keep_me_logged_in_for_1_year( $expirein ) {
    return 31556926; // 1 year in seconds
}