Most people do not stop acquiring new assets after they make an estate plan. They need to have an estate plan that takes later acquired assets into account and distributes them appropriately. There are many ways to do this and the best way depends on the specifics of your estate plan.
If your main tool for your estate plan is a Revocable Living Trust, you can acquire new assets in the name of the Trust instead of acquiring them in your own name. Doing so ensures that the new assets will be divided between your beneficiaries according to the terms of the Trust. A Pour Over Will is another way to makes sure that assets get divided according to the terms of the Trust. These Wills leave everything that is not otherwise distributed to the Trust.
If you do not use a Revocable Living Trust, then you will need to take extra care in your Will. The Will needs to have a remainder clause that states how any assets not mentioned are to be distributed. If you do not have a remainder clause, any property not mentioned will be divided by the court according to the laws of Intestate Succession, which usually means they go to your closest living family members whether you get along with those family members or not.