What to pack as in a case or shipping?
If shipping take everything or as much as you can get into your container. It is expensive to replace items here so unless you need soemthing new put in in the container. If you don't need it here then you can easily sell on ebay or gum tree.
If it your case you are packing it will depend on what time of year you land here and also who you are flying with for lugguage allowance.
As for who to tell and forms to complete:
Inland Revenue form P85
Child tax credits
Child benefit
National Insurance
Dr
Dentist
Milk, Papers etc
House insurance
Car insurance
DVLA if you can get some car tax back
Bank
Credit cards. Keep one open but tell them you may be spending in Australia
Phone
Internet
Mobiles
Sky or Virgin
The only thing that caught me out was not being prepared enough for our air freight. The additional costs when we went to collect it at the airport made it expensive. Those items, ie winter clothes could have been replaced for less money than it cost when our final air freight costs were added together.
Bring your tumble dryer or get one before you leave. They are very expensive here and you WILL need one.
Be prepared for the emotional pull if you have a leaving party and once normality sets in here. It is stressful and you will argue with your other half and if anything like us way more so than ever before. You do get through it though.
When you get here shop around for internet deals. We went with Telstra but a bit more research and we could have got a supplier cheaper. It's around $90 for an average internet connection per month here - again, not cheap. Your landline will always be telstra but you can shop around for a phone call provider. Unfortunatley, there are no comparison sites out here.
Car insurance we didn't find anything to beat Bingle and for home insurance it was Real Insurance.
Your gas and electic come from one supplier only so nothing to research there.
Mobiles are easy to come by, even on contract.