For your will, you will need to think about who is best suited to be your executor, and who should be your beneficiaries. You could look at parents, siblings, friends, or a corporate executor; for beneficiaries, that could be family members or a charity. If you don’t make a decision, however, the government will decide for you on both fronts.
What is even more important are your powers of attorney. If you don’t have them in place, your loved ones will have to have you formally declared incompetent in order to be able to act for you; also, a guardianship application can be quite expensive. If you are single, you need to think about who is best named in a power of attorney document so that you are protected if something happens to you and you are living, but unable to manage your affairs or direct your care.
Just because you aren’t married or don’t have children doesn’t mean you shouldn’t do a little planning.