If notes and favorite_sites have no relation then trying to combine them into
one query doesn't really seem to have much advantage. You could use a UNION
query as Dan suggested which will certainly give you something along the lines
of what you're after but it you'd have to consider what performance gain you
might expect from such a move - I'd imagine the differences in performance
would be almost non-existent.
Are you sure your performance is suffering because of the queries? Have you
turned on debugging and looked at the total execution time of all queries? I'd
be looking at other aspects of the page generation before trying to combine
queries - especially if the data isn't related.