You need to ask your local immigration office what their policy is. Each immigration office sets their own policy on this and it's not consistent across Thailand.
If you're in your home country then your driver's license if it has your address or a utility bill with your name and address on it. If you're in a foreign country then a hotel booking or passport entry stamp.
You need to get a re-entry permit before you leave, either from your immigration office or from the airport after you go through security. If you leave without this, everything you have done so far will be cancelled and you would return without anything and have to start over completely.