After doing my own research of what I need to know and take with me before I left for Bali and after being here for almost two months, these are the few things you absolutely need.
1. Your passport, your visa and travel insurance.
Obviously, your passport needs to be valid for another six months when entering Indonesia.
In case you want to stay more than two months in Bali, you need to apply for a visa at your local Indonesian Embassy or Consulate. Otherwise, you can opt for a Free Visa (30 days) or Visa on Arrival (30-60 days) after you land. Check my article on things to know when you arrive in Bali for more details.
I advise you to buy travel insurance from Allianz and you won’t have issues at the local hospitals.
2. Credit cards and cash
Two cards are better than one. One to withdraw money while in Indonesia, one for backup in case the first one is blocked by the issuing bank. The credit cards have a slight advantage over debit cards, but you won’t miss it.
USD has sligthy better street exchange rates than EUR or GBP.
3. Your favorite swimsuit
At least in Ubud you will have a hard time finding a nice and not very expensive swimsuit to go to the pool or spa. For the price of one you could buy five dresses or more! This is not the case for cities located near the ocean.
Other than this, take only your most personal items. In general you can find everything in Bali. Really, you can buy everything you want when you arrive. I left with just a few things in my backpack and I have yet to find one item I couldn’t have bought in Bali.