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You can sign up for good travel cards here; Monzo, a Revolut card OR a Wise card. These are the best rate cards for travelling.
Don't bother bringing cash - it's easy enough here to get money out. BCA, Mandiri, HSBC and BNI are all good atms to take money out of.
Get these at the airport or when you've just arrived. Telkomsel is the best carrier, take your passport with you when you grab one as they'll register you.
These are dotted everywhere, be careful with white clothes or anything expensive as they have been known to shrink stuff.
For a full shop I recommend heading to any; Popular, Pepito and Frestive. For snacks; Alfamart, Circle K etc
Go check out my guide for the best free things to do as well as itineraries and travel tips to make your trip unforgettable.