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/r9k/ and /int/ (not to mention s4s, bant, etc.) are good examples of boards with no theme where you just go to pretend you're doing something with your time.
Pick a hobby board and become genuinely interested in the hobby.
I'm not telling you to be productive in the mainstream sense of the word, but to do something that at leasts involve a smithereen of touch with what other people are doing.
You can read books or learn how to draw for a more "useful" hobby, but you can watch /a/nime or play /v/idya, it will still be an improvement compared to the nihilism from boards like /r9k/.
If these are too brain-intensive for you, just do some real-life, slow hobby, like raising animals or cooking, there are boards for that, too.
I am the complete opposite of you, I can go over /lgbt/ or /o/ right now and find something interesting to read about that will keep me entertained for hours, despite having nothing in common with these people.