That entire novel is written in a strong southern dialect, so words are written as the are spoken and not spelled correctly. However this is actually just a common way that people throughtout all English speaking countires pronounce the word "of" and might is just another way of saying it is possible he could of thought of that.

It is instead of 'have'. "I might have thought of that closet." It is just a colloquial way of speaking. Hope this helps Bob

In standard English, the full sentence would be this: 'I might have thought of this closet'. This is a common construction to refer to a possibility in the past: (1) modal verb : might (2) auxiliary verb: have (3) past participle of main verb: thought Similar construction are, for example 'I must have seen', 'I should have gone', 'I would have taken'. In speech, the 'have' is usually contracted - ''I might've thought of this closet' - and in rapid speech it is often reduced to a simple schwa syllable /ə/, which sounds the same as 'a'. If you think the 'a' as 'have', the grammar makes sense.

It's just a dialect of a southerner. "I mighta' thought of that closet" and some more examples "I shoulda done that" , "I coulda done that, but I ain't gonna" (I could have done that, but I am not going to). People use these a lot around where I live but it's basically a slang from the accent around here Texan.