Looks like the MARINE CORPS INDIVIDUAL RECORDS ADMINISTRATION MANUAL (SHORT TITLE: IRAM) is one good reference for some of these. CHAPTER 6 ABBREVIATIONS AND ACRONYMS begins on (actual document) Pg.# 6-3 (177 of 259 in PDF) and continues on to the list a few pages later.
das - DAYS
B&W - BREAD-WATER
CO - COMMANDING OFFICER
OH - OPERATIONAL HANDBOOK
fr - FROM
conf - CONFIDENTIAL