There are several definitions of ready which are light on the preparation side.
You have to be prepared to be ready, don't you? :wink:
- "Be prepared."
--Boy Scout motto
adj., -i·er, -i·est.
Prepared or available for service, action, or progress: I am ready to work. The soup will be ready in a minute. The pupils are ready to learn to read.
Mentally disposed; willing: He was ready to believe her.
Likely or about to do something: She is ready to retire.
Prompt in apprehending or reacting: a ready intelligence; a ready response.
Available: ready money.
tr.v., read·ied, read·y·ing, read·ies.
To cause to be ready.
Pope of the Dictionary.com Forum
I think any kind of readiness implies preparation. Certainly, someone who is ill-prepared is not ready. Possibly in some cases it has more to do with alertness than with preparation for a particular activity. In such a case a person might be said to be "ready for anything". If I am "ready, willing, and able" then I am prepared for whatever might come my way. Of course, the definitions of "ready" that don't have to do with people do not apply.
(Readiness in the case of the military means that they are prepared for combat.)