A letter of instruction can complement an estate plan and provide your loved ones with additional details about your assets and wishes after death. What goes in a letter of instruction?A letter of instruction is a cheat sheet for anyone involved in settling your affairs. Unlike a will, this letter has no legal authority. A letter of instruction is a document that lists all relevant financial information that your family members or executor need if something happens to you. Pet care: Instruct the executor what to do with any pets that were left behind. If you have pets, make sure they will be taken care of upon your death. Hypnotize Yourself Out of Pain Now!