HTTP cookie:设置值的准则

I couldn't find a clear answer to this question, hence me asking it here. Maybe I'm just looking in the wrong places...

What should I set my cookie value to?

After reading through RFC 6265, I could only find details such as:

 cookie-value      = *cookie-octet / ( DQUOTE *cookie-octet DQUOTE )
 cookie-octet      = %x21 / %x23-2B / %x2D-3A / %x3C-5B / %x5D-7E
                   ; US-ASCII characters excluding CTLs,
                   ; whitespace DQUOTE, comma, semicolon,
                   ; and backslash

and the below line makes me think I won't find any answers in that RFC:

The semantics of the cookie-value are not defined by this document.

I'd like to know if there are any standards for what a cookie value should be? Can it be as simple as abc123 or should it be a really long string of random characters?

Why?