Between the strenuous treks and meagre meals, you're probably going to lose a few pounds at Endau Rompin.
In Kampung Peta, meals are available at the canteen at the Park Headquarters. There is also an Orang Asli house near the jetty where most camping groups stop for supplies -- you may have a meal before taking the boat to Kuala Marong. Expect simple Malaysian food like rice, stir-fried veggies and chicken curry. They also have a fridge full of cold canned drinks, including beer.
If you are camping, you will need to bring your own food and cooking utensils, as well as a gas stove. Package tours will include all meals and your guide will carry the pack of cooking supplies. Expect lots of instant noodles and canned chicken curry.
Multi-day camping trips generally include as much bottled water as you can carry. When that's done, you can boil water and refill the bottles.
All garbage must be carried out from camp sites and disposed of at Kampung Peta.