Can you leave your backpack and personal belongings in your tent during the Rinjani summit climb?

Yes for replaceable bulk, no for anything you cannot afford to lose, and the decision should be made with your guide the evening before, not improvised at 02:15 in the dark. The summit push from the Sembalun rim starts around 02:30, and the camp will sit unattended for several hours while your group climbs, so what you leave behind and how you leave it matters.

The carry list is short and non-negotiable: your passport and cash, medication including any allergy treatment, your phone, a headlamp, water, and your warm and rain layers. Everything else, spare clothes, the sleeping bag, your duffel, toiletries, is a reasonable candidate to stay in the tent. Zipped fully closed, inside the tent rather than in the vestibule, with nothing food-scented visible through the mesh. Close the inner and the fly, and take the snack bag with you, because food is the one thing that will absolutely be investigated by the camp’s macaques while you are gone.

The question people forget to ask is who stays. On many departures a porter or assistant remains in camp, which is part of why the tents and camp gear are still there when you return, and our crews normally work this way. But camp presence is an operational detail, not a guarantee you should silently assume, so agree it explicitly: who remains, what they are watching, and whether your tent specifically is being watched or just the camp as a whole. A crew member in camp is a convenience and a deterrent, not a safe deposit box.

Our standing brief to guests is the honest version: we almost always have someone in camp, we have never had a serious theft problem, and we still tell everyone to take their documents and medication to the summit. The mountain has a way of testing assumptions, and the summit push is safer with a light pack of essentials on your back than with a nagging thought about what you left in an unzipped tent.