Definitely agree that clean water tops the list—you can have all the gadgets in the world, but if you don’t know how to make questionable water safe, you’re sunk fast. I’d probably put fire starting a close second, especially if you’re in a colder region or need to cook. What surprises me is how many folks overlook basic food skills, though. Even just learning three simple ways to preserve or store food can stretch your supplies and keep you fed if things get tight.
First aid is another that’s easy to put off, but it saved me more than once (one time with a nasty slice in the garden—would’ve been a mess without basic wound care knowledge). As for comms, I’d say it’s important, especially if you’re not solo. Even simple signaling or battery-powered radios can mean the difference between isolation and a lifeline.