What do you mean by glucose exactly? What kind of foods should I be eating? I usually just get whatever for lunch at my company - tacos, Indian food, whatever is being served.
A good heuristic is that if you bought it, or it was bought for you, it's got too much refined carbohydrate in it and the serving size is too large. This is because to consumers value=(volume*taste)/dollar
I'm not familiar with the effort required for mountain climbing, but eating a varied meal beforehand would help. Personally, a peanut butter sandwich, banana, half an avocado (depending on the size of the avocado), tall glass of milk, and celery with hummus will prepare me well for the following few hours. Adjust this for yourself as needed.
A healthy balance between fat, fiber, carbs, and protein is what you're looking for. I can't give any any hard numbers but a good macro-nutrient balance is the first step to a healthy diet, with the second step being fresh food.