I'm not as certain as some that he went to the reserve with the intention of simply killing himself. While I do agree suicide is probably the most likely manner of death, I'm open to other possibilities at this point. Drug taking (accidental overdose), insect/snake poisoning, injury, illness, drowning, wild animals, etc.
He apparently took a backpack, dry bag, notebook, possibly other personal belongings. The parents incidicated that they (might have been just Chris) looked for him for a few hours initially - if this was a known spot and he had killed himself straight away, they would have found his body easily. My guess is that if it was suicide, there was a period of time where his mental state deteriorated before he carried it out.
This case has also been so incredibly bizarre that it would not surprise me one bit if there are still further twists.