Footwear matters more than people expect. Sandals cover beaches and rice terrace walks fine, but if a Mount Batur sunrise trek is anywhere on your itinerary, bring proper closed shoes — that trail is loose volcanic rock, not the kind of surface flip-flops handle well in the dark.
Sun protection is non-negotiable, and reef-safe sunscreen specifically, since several beach areas actually restrict the regular kind. A hat and sunglasses round that out. If it's rainy season, November through March, a compact umbrella beats a bulky raincoat — the showers are heavy but short.

Don't skip insect repellent, especially for Ubud's rice paddies, and pack basic stomach medication just in case. A universal adapter is worth it too, since Indonesia runs on Type C and F plugs.

One thing a lot of first-timers get wrong: they over-pack for a destination that really doesn't need it. Bali isn't formal, and a good tour operator will usually tell you the same thing — pack light, pack breathable, and buy whatever you forgot at a local minimarket for a couple of dollars. That advice alone saves more suitcase space than any packing list ever could.

Get the basics right and the rest of your Bali tour takes care of itself.