We hope you ate well in Kota Kinabalu city -- it's pretty slim pickings around the mountain.
Inside the park itself you'll find Balsam Cafeteria (06:30-21:00) serving sandwiches, fried rice, and other quick dishes. The open-air setting is lovely, but the cafeteria can feel chaotic with groups of climbers scarfing down one last meal before hitting the mountain. Also inside the park, Liwagu Restaurant (08:00-21:30) is more formal but also more expensive, serving American breakfasts, Chinese food and seafood.
Just opposite the park entrance, Restoran Panataran Kinabalu (06:30-20:00) represents better value, serving up Malaysian curries, fried noodles, hot soups and stir-fried veggies from 6 ringgit, or buffet-style lunch for 12 ringgit per person. It's just 2 ringgit for coffee or tea and they also sell snacks, bottled drinks and basic groceries like bread and tinned chicken curry.
If you're staying at the Mountain Resthouse or Bayu Lodge, the staff can cook you simple meals.