I lived and traveled in Indonesia for six months and my vital equipment included nylon travel pants, a lightweight button-up polyester shirt, lightweight, quick drying hiking shoes (not boots), a cap, sunglasses, my ATM card, a credit card, a guide book, a battery powered travel fan (because it's oppressively hot and humid 24/7), Imodium AD, and bug spray, which is my answer to your question.
If you bring your cell phone you'll have to buy a new SIM card over there and switch it out to get it to work, but I got by without one, using internet cafes to stay in touch with friends and family. I didn't need GPS, water purifiers, knives, mosquito nets, battery powered shower pumps, security belts, or any thing else. I also never carried more than $100 of the local currency in cash, most of the time much less, using a credit card to pay for things like groceries in larger stores, hotels, and restaurants.