Hi, Abbel - and Twink! Yes, I'm currently in Jakarta. Life here is totally different to that the UK or other western countries. My main bit of advice is to be prepared for nothing to work properly! Services are not reliable, water/electricity/phone going off at times and consumer goods, if locally produced, can be iffy. Also, don't expect anything to happen quickly. It might, but you can't rely on it - Indonesia runs on 'jam karet' which translates as 'rubber time'!
I don't think there are any essentials you need to bring with you as just about anything is available, although UK food stuffs are an exception. We bring Marmite with us as it's almost impossible to get the UK version. Most western food stuffs are in fact US or OZ versions so don't taste like UK foods anyway. There are plenty of supermarkets and shopping malls around. Tap water is not suitable for drinking or cooking or even cleaning your teeth. Bottled water comes in big containers, inserted into a cooler and that's what you use instead.
Medical facilites, if you use an expat clinic, are fine, though if you need an op you will have to be evacuated to Singapore.
Safety has a very low priority here. We never touch the electrical bits in our apartment, always get maintenance to do it, as the Indonesian concept of wiring is a bit different to ours. You may need to get seat belts installed into the back of your car for the children as rear belts aren't a requirement here. You can buy child car seats here if you don't want to bring them with you. Be prepared to spend a lot of time in the car. No one walks anywhere as it is too hot and polluted and the roads are clogged with traffic all the time. Tonight we spent 2 hrs travelling the 6 miles home from the mall!!
Personal safety is a big issue and we are quite restricted in our movements at the moment after the Bali bomb and with the ongoing Iraq situation, of course. That varies, depending on current security concerns. The Embassies email updates and so on, telling you what's what. There are a lot of does and don'ts, such as don't use public transport or visit certain areas. Always have the correct documention with you, such as passport & KITAS copies and your police card. Be careful about what you wear and how you address people. Indonesians are a very polite society and get upset over any slights, real or imagined. 'Saving face' is a very big deal indeed. At the same time, they don't like to disappoint or say no so when answering a question will tell you what they think you want to hear, not the true response! There are quite a lot of religious and other customs to get acquainted with as well, such as not using your left hand to give or receive things etc.
When employing staff they may try to take advantage of you, asking for loans (which never get repaid) or simply stealing from you. It's better to get staff via personal recommendation - agencies sometimes run scams, using the maid as a conduit for access to your home and possessions. Staff tend not to be proactive. Unless told, a cook may not substitute carrots for peas, if there were none of latter but plenty of the former. If you employ a nanny, she may not have the same safety issues as you. For instance, unless you tell her that the children are not allowed to play with matches, she won't stop them if they find a box lying about!! However, there are training courses available on which you can send staff and speaking personally, we have lovely staff.
I'm sure this might all seem daunting but we are enjoying our life out here. It can be frustrating at times but it is also very rewarding. Indonesians are extremely friendly, they love to talk to you and will make a fuss of the children (you might have to put up with the chldren being touched on the cheek as it is considered good luck to pinch white flesh!). I shall definitely miss it when we come to leave.
There are loads more things I could say but instead I'll direct you to an expat website Indonesia info which is really useful. When you get here it is almost essential to join at least one of the societies here, the Australian and New Zealand Women's Association, the British Womens's Assoc or one of the smaller ones (you don't have to be the relevant nationality to join them). They offer lots of services and contacts and there is always someone to help newcomers settle in. HTH!