From "The Officer's Guide" - 1942
Officers' Field Bag, or Musette Bag. The officers' field bag is the container in which he carries personal items of equipment to provide for his necessities and comforts while on the march, away from the base camp or bivouac, and in the absence of his bedding roll. It is a necessary and convenient article. The officer will wish to have with him facilities with which to eat, a minimum of articles with which to wash and shave, some articles of clothing for replacement, and other small conveniences. On field service never let yourself become separated from your musette bag! The truck with bedding rolls may not come forward, or it may go astray; but if you have the essentials with you some of the discomforts are avoidable
Many officers overload this bag. It then becomes a burden. But it is better to overload it somewhat than to leave out essentials. No list could be prepared which would suit all users. It would be difficult, however, to omit any of the articles listed as follows: Meat can, knife, fork and spoon, (the canteen cup is carried elsewhere.) Tooth brush and powder (not cream.) A comb. Your favorite shaving equipment; some prefer a jar of brushless cream instead of the soap stick. A cake of soap and a good quality small towel. Extra socks. Small can of foot powder. Two extra handkerchiefs. A light weight wool sweater to wear under the shirt. A good flashlight with adequate battery capacity and an extra bulb. A small roll of toilet paper. A bar of unsweetened or slightly sweetened chocolate may bridge a gap between meals. Many officers roll the raincoat tightly and insert in it the field bag. Some officers include the very light weight, oil-silk, golf-style rain jacket or windbreaker for wear under the shirt or other outer garment. Add to this your own particular choice of "chigger-bite" and mosquito remedies and you will have most of the real essentials. After the first long march and cold, rainy night in which the baggage does not come forward the necessities will separate themselves from the non-essentials.