I used to have this problem myself, and the main cause, I think, was a lack of direction. Now I have one, and I discard any piece of info that doesn't concern me, instead of trying to read everything because "it may come in handy".
Assange's typical breakfast while in exile? Yeah, whatever. New distributed computing paradigm? Can wait till proven useful. Uber vs. Lyft? Don't care, using neither. Foreign news? Whatever. Someone got harassed by authorities/uber driver/whoever? Nothing I can do about it. Rant about poor customer support? Them's the breaks. "What I learned" articles? Good for them, don't care. Article about some random niche (e.g. most prolific zipper brand)? Will read first paragraph, tops. Inspirational blog post about "the one thing holding you back"? Bleh, probably wrong in my case, we each have our own obstacles.
I still have hobbies and interests, and feed them, but to anything that's not related I don't even give a second look. I ignore everything related to tech I neither currently use nor particularly like, as well as any "lifehack" article (ooh, 0.5s off my showering time!), or an overly opinionated piece (any of these words in the title: incredible, insane, unbelievable, horrible etc. See cracked.com).
Also, nothing by any writers condescending enough to talk about their reader as if they know him/her in their articles ("the reason you...", "you must..", "you know...", "of course, you may..." - no, that may not be the reason I, that may not be what I must, I may or may not know, and of course, maybe I may not).
So the main takeaway, I guess, is to question whether each and every one of those instapaper/pinboard articles really matter to you. I used to be a big hoarder myself, and wondering when I'll get through it all, but I realized I'm doing just fine not doing so. Sure, let them gather up! Have a 100-item, 1000-item, 1000000-item backlog, what of it? You'll have something to do when bored, but until then, leave them be, and don't dare look at how many are there (it doesn't matter, you'll never clear it anyway).
I still hoard BTW, but just because doing so gives me the sense that "I won't be missing anything, I'll get back to it". I won't, of course, but my lizard brain doesn't know that, so shhh!
As for books, just forget about them. Leave that list aside and only look at it when you feel like reading a book and wondering what to pick up next, and never look at how many are left. May be hard at first, but you may eventually learn to just "let go".
Misc techniques I found useful:
Speed reading - read only the first few words of each paragraph, good articles are well-divided in paragraphs, and you can skip the crap. Generally, I skip case studies, unless the subject particularly interests me - the conclusion may be proven flawed in a few years anyway, once a disruptive element will enter the equation - "How could real estate possibly be a bad investment? Look at these case studies showing how reliable an investment it is!".
Shortlist - make a list of interests (not more than 10, including job-related stuff, and be specific. Say "Northbridge", not "IT and stuff..."), discard everything not related.
Next! - if an article keeps repeating the same thing for several paragraphs ("since they're successful", "because they're successful", "have successfully..."), it's a red flag that it probably doesn't have much content, is just filling up a word quota, and may have even given away the conclusion in the title (as a hook for the reader). Skip to the last paragraph, then move on.
tl;dr
Discard the irrelevant, filter your knowledge input, get used to there always being more out there to read, and to being unable to absorb it all. Disregard how much there's left to read ("oh no, 1000 more news items to go!"), and skip over the boring and the trite. Anything that doesn't help you, your family/friends or your career, and anything you cannot do anything about (natural disasters, conflicts in foreign countries - odds are you won't remember these yourself in a couple of years, remember how many other things you'll get to read about until then), you can do without.