I will remind that Internet Archive data dumps of the whole Stack Exchange network. See also this blog post: Stack Exchange Creative Commons data now hosted by the InternetArchive. (Possibly you might be able to find also some older versions, see here: All Stack Exchange data dumps. Some related discussions on this meta: Public dumps for mathoverflow? and Long-term archiving of MathOverflow.) Of course, if a question gets deleted in the interval between the two archival dates, then it does not appear in any of the dumps.
You could also get all your questions, posts, comments from SEDE. Various queries can be found in the answers here: Dump of my own Stack Exchange content, Backup, save, download all questions and answers for individual users.
If you want to export in some reasonable way a single question, a favorite solution seems to be StackPrinter. See also: How do I know I won't lose all my work in math.SE?, Save the answer in PDF?, Is it possible to convert (and possibly download) the answers/discussions in pdf format?