Lots of places hire out the inner tubes. If it has been raining heavily than the river becomes swollen, this makes rafting very exciting and also very dangerous. I can vouch for this from personal experience. The park wardens use shoulder bags to carry the food to feed the orangutans. An orangutan may assume that your bag contains food and snatch the bag from you.
Orangutans are much stronger than humans and also bite.
Good chance to see orangutan in the jungle and at the rehabilitation center. Go jungle trekking.