I have done some 90 minutes pieces of strenuous exercise without any problems on this diet. There are lots of sites that will let you estimate how many calories your hike will burn. You might decide to increase you intake by this amount less that of 15,000 steps.
Cheese should keep okay for a few days and many vegetables will keep, such as peppers or carrots. Apples should be okay. Do you have cooking facilities? If so you could take dried beans.
Or you could just decide to eat more vegetables on the first day or two (falafel, onion bhaji salad, carrots cut them up as you go) and on the 3rd and 4th day you don’t eat as many vegetables as normal. You could take some higher fibre snacks such as prunes, and guilt free brownies, or something else made from coconut flour and have these on the final days.