How do you deal with the endless stream of interruptions that we have nowadays?

Well. If social media are a distraction to you, and this extends to your desktop usage, you are in a kind of pickle. However, you are literally interrupting yourself. Which isn't the same as fending off notifications.
After I noticed that smartphones were disrupting my life and workflow, I did a simple thing. Removed all social apps and games from said phones. My main smartphone doesn't even have a SIM card, and I mainly use it as a book reader / music player.
But for you, I would recommend this: put your social apps on a phone or tablet, and leave your "social device" out of reach while working. Make a habit of browsing these social sites on a device other than your work computer.
What is your workflow like? Does it have a regular structure? Working on content I don't easily get distracted. Each task is like a meal (research => design => implement => test => polish and commit) so erm. I kinda think this structure helps me stay focused. Obviously not all work is so neatly laid out (which is fine) but what I mean is, when that structure breaks down, I'm more likely to get distracted.
Another thing. When getting distracted, go for a walk. For some people this works well (not everybody).

Pomodoro technique is the way to go for me, I find extremely difficult to be concentrated for 1 hour or more, if the task is hard it's natural for your mind to wander, so let it wander for a while, another thing I think works is to remove your distractions

I turn off PC notifications, then I check slack periodically when I feel like (I've 3 monitors and the slack is always opened on a part of one).
Educate people to use ticket service instead rushing into IT department which is a bad practice unless something is burning.

Also earbuds with Spotify or Youtube are a must. if you want to say me something use slack, hangouts, come here and let's talk, this avoids people from shouting from side to side of the department disturbing others.

Of course it's nice to keep conversations with our colleagues while at work and the concentration needs are less than average, not having human contact causes depression so don't forget that.

I block social media websites on my /etc/hosts file. Eventually I have to unblock them because important resources are also published there, so it's a never-ending game.

Slack is the thing that interrupts me the most, we have messages coming through every few minutes and sometimes I'm mentioned in threads which never seem to end. The Slack calling feature is also really annoying because sometimes people just call instead of scheduling a time and when it happens while I'm trying to debug something complex it takes me at least an hour to get back to where I was and make more progress. I'm more productive on days when things are quiet.

Yes there is simple solution that works for me - turn it off.

That's a great idea, thanks for sharing!