Example for me: 2 day hunt. 3,000 feet elevation gained and loss per day. 8K feet and higher. 2100 calories of food per day.
Day before hunt: 3500 calories with 50g net carbs (my threshold for ketosis)
Day of hunt: 3 tbsp Butter in my coffee for first "meal" roughly 11am and 1 apple. 1 avocado & 2tbsp almond butter with 2 strips of bacon 4pm. Dinner 1 hour before bed, home made keto chicken thigh chilli (broccoli, chicken thigh, ground sausage, carrots, chicken stock).
Now you must be careful about how much LESS you eat than you burn. In ketosis, you will be burning body fat as fuel for your BRAIN but not your muscles. You want to remember to always provide your body what it needs to repair and continue. Your brain takes up something like 40% of your caloric intake. I walk around eating around 2500 calories per day, Im very active and work out daily. When I hunt, Im more sedentary during glassing periods. Hiking with a pack does burn calories, and longer periods of movement will increase what you burn, but if you already have more than 10% body fat, you'll be able to account for what your brain needs. So if you take 40% of 2500 =thats 1,000 calories. So you would need to eat 1500 to get to 2500 total. If you do that, you'll loose 1lb of fat every 3 ish days. Now add in your hours of hiking and lets say thats 8 hours, and lets estimate (example only) you do 100 calories per hour. You would need to eat 1500 for maintenance and add in 800 more for energy spent. that would put you around 2300 calories. You'll be safely in a deficit.
Couple more things to remember. When your adapting to ketosis, your body has a tough time regulating heat. So dont do this and expect to be warm in the cold, if your not already adapted. Also everyone is different. If you dont have a way to measure your ketone or blood, then sorry but your most likely eating low carb and long term you can cause hormone issues. Best way to do it, measure your self, find out what your max carb load and protein load can be, for me thats 50 net carbs on normal days and 125 net carbs on extreme days, and roughly .8 protein to lbs without any loss in ketosis or energy.