Most of the time, you must stop your contracts (water, electricity, telephone,
rent, TV,…) by sending a letter. If you pay your bills by standing order,
don't forget to tell your bank about your departure.
Just as you need to complete forms when you leave, you will need to fill in
forms when you return. The easiest way is to contact the consulate where you
are registered to sort out your situation. You will have to establish a fully
detailed inventory of your furniture. A moving form attestation is often demanded
when you pass the border (you can ask for it at your Consulate).
You will have to think about school registration
if you have children.