Don't reuse material you have contributed to Wikipedia (or other sources where you aren't clearly attributed).
It's too difficult to establish that you are the source of the Wikipedia material (and in some cases impossible). Some authors are anonymous or use pseudonyms. In addition, content on Wikipedia often can't be straightforwardly attributed to one author, due to the community process of creating and revising text.
A further problem is that most Wikipedia content is under a license that allows redistribution "if and only if the copied version is made available on the same terms to others and acknowledgment of the authors of the Wikipedia article used is included". In many cases this will not be compatible with the terms of a journal you wish to publish in.
Wikipedia is very commonly used and very easy to find, and if someone does find it, it raises unnecessary ethical concerns. Even if you believe that there is no actual problem and you are able to provide evidence of that, it is simply best to avoid any suspicion of wrongdoing on this. Someone might get the wrong impression, and you might not have a chance to correct it (for example, what if a hiring committee finds it and assumes you have plagiarised, discarding your application?).
Therefore, I would simply avoid this. Even though in some cases it would be technically allowable, it would raise too many possible concrens. If you need content similar to what you have previously written up on Wikipedia, just rewrite it.
Reusing material from other sources like blogs is less clear.
There isn't an absolute ethical rule against republishing your own material. However, claiming something it is new when it is actually recycled typically is a problem. This is sometimes called "self-plagiarism" (though that term is controversial). Wikipedia has more detail on this.
Journals typically expect your paper submission to be previously unpublished work. However, whether previously publishing something informally on a blog falls afoul of this requirement is a gray area, and probably dependent on individual journal policies.
If you want to reuse some material from a blog or similar source, be sure you know the policy of the journal you are publishing. Contacting an editor would be a good idea if you aren't sure.
In some cases you may be able to reference your blog post, though whether that is considered an acceptable source to cite will also probably be journal-dependent.