I’m a note to a friend and a national monument, but I fit within an envelope. What am I?

What do you drop when you need it, and pick up when you don’t?

Along with thoughts, I transfer ideas to paper. Shape and size can vary quite a bit, and my price can be cheap, or more than a house. I hold liquid, as we no longer chisel; what is this tool you hold?

The youngest princess doesn't like me very much. I fetched her toy, and she won't let me touch her plate, not one bite. I'm not allowed on her pillow at night, that's it! Hatchet's not buried. Guess we'll never get married!

I have a waist but no ribs or spine. You turn me upside down by design. I measure your moments in a narrow line.