You will need a synopsis. It's a good idea to do more than one--a one-pager and a five-pager, for instance, since different agents may have different wants. A brief bio is also good to have.
The kind of publisher an agent would place you with will create the back cover blurb itself (often with your input) so that's not something you should need (and if an agent asks for it, be wary). I also don't see the point of a character list, since if an agent or publisher is interested in your book, they'll read it and discover the characters for themselves, and if they're not interested, a character list will make no difference. You also don't need an author photo at this stage of the game, though if you get a contract offer, the publisher will probably ask you for one at some point.
For fiction, and for the kinds of publishers an agent will submit to, you do not need a marketing statement or marketing plan. Smaller publishers often request this, because they rely more heavily on their authors for marketing. But big publishers and larger independents will not ask for such a thing. If an agent requests this as part of your submission package, take a close look at his or her track record--he or she may be working only or mainly with smaller publishers (for which you may not even need an agent).
Obvously, if you have a huge platform on social media that relates to your book, or some other meaningful PR advantage, it makes sense to mention it in the section of the query where you briefly mention your credentials. And once you've signed a publishing contract, the publisher will give you a marketing questionnaire with all kinds of questions about local bookstores it could target, media outlets you have connections with, who they can approach for blurbs, and the like. But you don't need any of that at the query stage.
- Victoria