I think there's a substantial difference between the knowledge required of a med student vs. intern, but...
Read the appropriate chapters in Essentials of General Surgery by Lawrence or Essentials of Surgery by Baker and Stucchi. Know the Q&A in Surgical Recall by heart. It's more important to know the basics cold (doing your ABCDEs correctly) than the different grades of a spleen/liver injury. If you're following a patient and interested in surgery, consider reading a chapter in a resident level text (Greenfield, Sabiston, etc.) for the relevant injury. The Trauma textbook by Feliciano is the next step. Interns should know ATLS, but a lot of it is ATLS is gained through experience as a med student.
Trauma is a lot of algorhtims. But you always start with your Airway (they breathe on their own or you intubate them- rare case crich them), you check their Breathing (i.e. do they have am obvious pneumo/hemothorax requiring a chest tube, if they're intubated, you breathe for them), and then you do Circulation (check a blood pressure- two large bore IVs and give fluid- if the BP sucks, think O negative blood- if they have a gushing bleed, someone applies pressure). Then check for Disability (GCS, pelvic stability, and then log roll to assess for spinal injury) after Exposing them. With enough people, ABC happen simultaneously. Then chest X-ray, likely pelvis x-ray. Maybe a FAST (Focused Assesment with Sono for Trauma) for a blunt trauma.
Nothing should get in the way of the initial trauma eval.
After that, the thinking begins. Of if it's a gunshot wound to the abdomen, the ride to the OR.
I'd separate critical care from the initial trauma resuscitation. The same basic books are good for the ICU. The finer points, however, are much more controversial and vary from trauma center to trauma center. The ICU Book is good but could still get you in trouble (Marino writes convincingly about the utility of colloid fluid- but if you order that in trauma surgery you will become a trauma).
ACS Surgery is more applicable for trauma critical care.