I make plans and strategies on how to defeat the titans based on Sun Tzu's "Art of War", I think how would the Walls and the 3DMG would influence warfare, politcs, religion and society in general after/if humanity gets rid of the titans and I try to guess where could the Walls be if, of course, SnK, happens on an alternate Earth. As for things that don't have to do with SnK, I do lots of things.
I think about how it would influence society too. The economy would collapse under the weight of medical expenses from having to remove people's kneecaps from their own asses and surgeries to fix clavicles which somehow ended on the wrong side of the body. Society in will live in general fear of having a random guy (specially dumb teenagers with no notion of consequences) violently burst through their windows into their dinner tables and loved ones. The market for apartments would collapse due to said fear and because of the structural damage buildings will take due to consistently having hooks piercing them deep enough to sustain the weight of full grown adults moving at high speeds. Since people would stop living in apartment buildings there will be slight additional strain on the environment due to the extra amount of people spreading horizontally rather than vertically. Teenage mortality would take an additional spike when they start jumping from buildings daring each other to break the fall with the 3D gear last. Congress meetings will take interesting turns. The occurrence of "accidental" malfunctions of the 3D gear in which hooks just happen to go through opponents adam's apples will be suspiciously high but since they are politicians no one will bother to question it just as they won't question why they allow 3D gears into the damn place.
Religion will take many different approaches to it. The more mainstream ones will forbid it due to the probable danger it causes to the user and those around them. Others will embrace it and use it for their initiations and rituals.
hunting and fishing will change dramatically. Rather than guns people will prefer to snipe their game with the hooks because why not. The damage to the animal population will be offset by the amount of people dying in the woods or drowning which will provide food for the ecosystem.
The 3DMWI will be invented. It will be a law against 3D maneuvering while intoxicated. God knows people will want to use the 3D gear while under the effect of all drugs known to man because we all know it would feel awesome.
And don't get me started on people wanting to do the nasty while 3Diing.... The injuries from those will upset even the most seasoned surgeon stomachs.....
Other than that, well, there are other manga. I generally try to find a manga release for each day of the week to keep me going.