Making a Will is not about wealth it is about making sure that what you want to happen to your estate does happen. It gives you the opportunity to specify such things as who will administer your estate, who will care for your children and who will receive specific items of your property.
The term 'residuary estate' or 'residue' refers to everything left over after you have paid your debts and the costs of administering your estate and given any specific or pecuniary legacies. It includes everything else you own. Usually you will be giving this to one person such as your spouse or to a group of people such as your children.
At its most simple the will could say, 'I give everything else I own to my wife.' Your wife will then receive everything left over after paying the liabilities and specific and pecuniary legacies.
A better way of expressing it is to say, 'After payment of my just debts, funeral and testamentary expenses and the legacies given by this will I leave all the rest of my property of whatever kind to my wife.'
It is important that you dispose of your entire estate correctly.
If you make errors so as to leave some part of your estate undisposed of, a partial intestacy will arise. This means that the legacies in your will take effect but the undisposed of part goes to whoever would inherit your estate under the intestacy rules.