If you are a pet parent, you'll feel better knowing you've done the planning to protect your pet after your death. A letter of instruction is also a helpful resource for executors.Once it is created, the next question is, where should you put it? Although the creation of a "pet trust" is. What goes in a letter of instruction? Providing for your Pets in your Will – Sample Will provisions and Pet Trusts. Fill out your free custom Pet Trust document - guided step-by-step! 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. Interviewer may fill out the application. Potential ineligibility set out in the letter.