(1) Metal materials are hard and firm, while inorganic nonmetallic materials such as ceramics and glass are hard and fragile. Therefore, tableware made of metal materials with good thermal conductivity and not easy to break should be carried;

(2) The external flame is in full contact with air, and the temperature is the highest when burning. Therefore, when the picnic pot is heated, it should be adjusted to a suitable height and heated by external flame;

(3) According to the nutrients contained in common foods, the above staple foods and side dishes mainly contain nutrients such as protein, sugar, oil, inorganic salts and water. From a nutritional point of view, there is still a lack of vitamins. You can prepare another vegetable, such as cucumber.

(4) The condition of full combustion is to increase the oxygen concentration and increase the contact area between combustible materials and oxygen. As we all know, if the "stove" is quickly filled with dead branches after the fine dead branches are lit, the contact area between combustible materials and oxygen is small, and the combustion is insufficient, resulting in a large amount of smoke. It shows that the condition of full combustion of substances is to increase the contact area with oxygen.

So, the answer is: (1) a; (2) heating with external flame; (3) sugar; c； (4) Sufficient oxygen.