Not strictly an expat related topic, but many expats start their Indonesian adventure with a holiday, and the thread has a lot of handy tips for new expats.
The backpacker's guide.
Never leave your passport with anyone for any reason.
Hotels should photocopy and return it
Keep it light, preferably hand luggage size; saves a ton of messing around at airports.
Pack simple (I know this is harder for girls).
2 pairs of very lightweight trousers.
A bunch of T shirts (It gets hot here so you'll find yourself using at least two per day)
One polo shirt (You'll need this if you visit immigration/other offices as you may not be allowed in without a shirt with a collar and long trousers)
Underwear/socks
I also carry a thermal shirt for colder areas/use on buses and trains (They're totally mad with the air conditioning)
A waterproof coat (Also handy if you're returning home to a cold country/going to cold areas of Indonesia)
A folding baseball cap (The sun kills me if I don't use one)
A roll of soft paper kitchen towels (Don't ask, just thank me later)
A pack of wet tissues - Many washrooms don't have soap.
A microfiber towel
A couple of black bin liners - when you first visit a bus rest stop toilet/washroom, you'll understand. The floor are often soaking wet and there's rarely anywhere to hang your bag/clothes.
A super light sleeping bag - make it yourself.
Take a piece of thin cotton material, at least one meter wide and two and a half times your height.
Sew it to turn it into a long bag, open at one end only.
Many budget hotels have no bed sheets but they do have free biting insects - sleep in that and you'll save yourself a world of grief.
I still carry mine when I wander.
Tip - squirt insect repellent on the outside at the open end and the ants won't walk inside.
Tip - This can also be used as a wrap to keep you warm on buses and trains.
When you arrive, go directly to Alfamart and buy:
a folding travel toothbrush (Rp10,00)
Small sachets of shampoo (About Rp1,00/each)
a bar of soap (Rp 3,000)
Many budget hotels don't provide these.
Suncream (if required)
Small sachets or a small tube of insect repellent (you'll need those at night)
Pack that lot into a light rucksack (without a frame), and you're good for a week or more.
Laundry in the most expensive places is Rp10,000/kg for next day service.
Use a waist hidden wallet for your passport, all your credit cards and larger amounts of cash, leaving only a smaller amount for daily use.
I use a neck wallet for that as it's very easy to get to but hard to steal from without you noticing.
Careful on buses and trains - keep your stuff close and cash out of sight. When the bus stops for a break - take your stuff with you.
I always book two seats on the bus - that way you can stretch out or even lie down on the seat; your soft backpack is handy as a pillow.
Always use an air conditioned bus. If it gets too cold, use the home made sleeping bag to stay warm.
Cross country train seats are wide - one is fine.
In most of Indonesia, air conditioned rooms are best, but you won't need hot water.
In cold areas (Such as Wonosobo), you won't need the air con but hot water is a serious bonus.