You'd have to use the Stack Exchange user ID: http://stackexchange.com/users/login.
This is the account_id, to be more precise.
With that, run the User's associated accounts method.
Iterate through the results running another query (with your user_id in each site) to build the favorites:
"site_name": "Stack Overflow",
I'm trying to setup http://stack2rss.stackexchange.com/ to receive full-body "responses" (comments, edits, answers and so on) to my own stackoverflow questions via RSS, but I can't find the right method.
Unfortunately there is no method that allows Stack2RSS to fetch questions, comments, and answers for your posts.
... clearly it doesn't work, since ...
There are separate RSS feeds for Hot/Week/Month, etc. EG:
The API /questions route offers equivalent sorting options for Hot/Week/Month. EG:
This is most likely one of those things you'll have to do yourself and one reason why the API is available.
And, it's not too hard; here is pseudo code that works:
Call /questions/featured with max page-size and (ideally) filtered by your tag(s) of interest. EG:
Page through the results until has_more ...