Best short riddles

Everyone has me but nobody can lose me. What am I?

There was a railroad crossing without any cars and trucks! Can you spell that without using any "R"?

They have not flesh, nor feathers, nor scales, nor bone. Yet they have fingers and thumbs of their own. What are they?

When you don't have me, you want me, but when you do have me, you want to give me away. What am I?

Slayer of regrets, old and new, sought by many, found by few. What am I?

I have no life, but I can die, what am I?

What has four legs, but can't walk?

I hiss. I can be poisonous. I am long. I have a forked tongue. What am I?

I have keys but no locks. I have a space but no room. You can enter, but can't go outside. What am I?

It can fill a room without occupying space. What is that?