I hope you're well aware that simply deleting your posts does nothing to erase them from the public domain. In fact, in some form or another you can never remove the things you have posted. Reddit regularly works with law enforcement officials and retains all saved data that you had deleted and will hand it over to those that wish to do you harm.
But I said things I don't want used against me!
Well, you're mostly fucked but you can do yourself a favor. Go to each of your posts, and edit them. Put anything down that isn't what you originally posted, and save it. Do that again. And again, for each post. Leave so little as to make each post appear blank. Gibberish won't help you as much as blankness.
At that point, you may delete your posts. Reddit will only be able to provide the saved information, which would be relatively blank.
Just hope that the third parties that save all reddit posts are not also called upon to share your unedited posts.
Here's a python script on github that will go through and edit your comments then delete them. You'll need to edit shreddit.cfg. There are some firefox scripts that will do the same thing.