How can you declare legally what happens to your body on death and what items you want cremated with you? Does that go in a will?

I am very solitary and concerned that I will die without any friends or family to make sure my wishes are respected. What is the closest I can get to ensuring that I am cremated with the ashes of my dogs as well as some photos/drawings and a throw blanket? If a state worker is handling this should I put all the items in one place because they might not care enough to search my residence for the items?

I'm in USA - California if that changes anything.

I know it's not healthy but the idea of some of my treasured dog items rotting in a landfill or getting damaged/soiled by a stranger is bringing me a lot of dread.