While my rewatch of the series is fresh in mind, I thought it'd be interesting to consider many of the times Walt had a possible path to a happier ending, but his poor decisions and dumbassery had lasting effects that came back to bite him in the ass. Though I do recognize that I am looking at this as if they were actual events. As long as they're in a TV show, absolutely whatever path was taken would've seen new obstacles pop up.
Near the start of the show, Walt could've accepted the help/job offer from Gretchen and Elliott. A legitimate source of income, and an alternate use for that big chemistry jones.
But if not that
He could've not jumped the gun on lacking evidence and started planning on killing Tuco. This could keep him from becoming an enemy of the Salamancas in general, which was... all kinds of trouble.
But if not that
He could've stopped pushing Jesse to expand his territory. If Combo doesn't die, the chain of events leading to things falling apart with Fring doesn't happen.
But if not that
He could've tried to prevent Jane from dying. What would happen afterward is a wildcard, but either Jesse and Jane going off to spend lots of money or just Jesse and Jane sticking around Albuquerque preventing Jesse from meeting Andrea, would result in fewer problems for Walt down the road.
But if not that
He could've been less a dick to Jesse at times like when Jesse was trying to go back into business on his own. Jesse is a pretty loyal dude to those that give him half a reason, so Jesse wouldn't come up with his "If I get caught, I'll trade my freedom for Heisenberg" plan. Walt could stay retired from meth without a large amount of risk.
But if not that
If all the stuff still goes down with the rival dealers and the death of Gale, it's still possible he and Fring could come to a working arrangement. Fring seemed to make peace with Jesse, and though it was probably part of his effort to get Jesse to switch allegiances, as long as Jesse and Walt stuck together Fring still wouldn't want to get rid of them anytime soon.
But if not that
He could at least not disparage Gale's work in front of Hank, causing Hank to continue investigating Gale and eventually Fring.
But if not that
He could leave well enough alone after the death of Fring. Mike's guys are in jail staying shut up. Walt is left without much money, but compared to the start of the series his family has gained a car wash, which isn't nothing.
But if not that
Don't leave Gale's gifted copy of Leaves of Grass in your bathroom, dumbass!