If you see string arguments and parameters getting cut off like this:
#0 hook.php(324): output_notice('checkout_before...')
#1 hook.php(348): invoke_hook('checkout_before...', Array)
You can increase the maximum length of arguments and parameters in the printed trace through an PHP INI setting:
<?php
ini_set('zend.exception_string_param_max_len', 100);
debug_print_backtrace();
?>
…so you can read the full arguments:
#0 hook.php(324): output_notice('checkout_before_payment')
#1 hook.php(348): invoke_hook('checkout_before_payment', Array)
In edge cases, it might even uncover nested traces that you didn't notice before.