The letter can set out details as to who should receive particular items and, in some cases, clearly identify the item. It may refer to special arrangements concerning the funeral service. However, you should always be aware that guidance concerning funeral arrangements should be given far in advance, as it may be some time before the will or letter of wishes is found.
It may also contain guidance to the guardians of minor children, concerning how you might want your children brought up in terms of education, religion or residence.
It is usually better to keep these specific requests in a separate document from the will so that they can easily be amended should the need arise.