You could barter out access to land in exchange for mutual defense.
Any sort of real collapse is going to be accompanied by a lack of diesel and there aren't a whole lot of draft animals around, so farming is probably going to involve quite a lot of human labor.
If I were to prepare for an apocalypse scenario, I would hoard bottled water, canned food, ammunition, and fuel. Roughly prioritised in that order. Possibly also batteries.
I feel like these are the things that will become scarce and valuable. Or at least help survival (food/water + ammunition). This makes them useful to me and also useful for bartering.
Of course, my stash needs to be safe both from the apocalypse scenario itself (will it still be in usable condition after a nuclear explosion, for example?) and from other survivors. It also needs to be somewhere I can actually get to it (safely). This, coupled with the fact that I would need large enough quantities of these items makes it rather difficult.
But, regardless, that is my I haven't done anything about it and likely never will plan to survive the apocalypse.
Also basic medicine/medical supplies. It's a staple plotline in apocalyptic fiction but it seems legit for any natural disaster or major civil unrest as well. Whether you're stuck out in a remote location for safety or in the middle of the aftermath of a natural disaster, having a good first aid kit and a supply of medication could save the life of you or someone else in need.
The only bit that seems difficult (but again, this is from apocalyptic fiction so grain of salt) is that so many important medications like insulin, antibiotics, and strong painkillers can't just be purchased at generic wholesale and kept for use or trade in major emergencies or times of real hardship. In the stories it's always the pharmacies that get looted first and there's always some chapter or episode where a family member or friend is sick/injured and the characters desperately need to find antibiotics or insulin or the like.
I understand that this is a bit silly going from fiction but those stories are appealing because they get you to think about how you would deal with life-threatening challenges. In a way it's odd that we have all of these important and effective medicines but whether the emergency services and doctors are blown to smithereens, bitten by zombies, or just overwhelmed with patients after an epic earthquake/flood/eruption there's really no way to access them without looting or black market.
I just know that in the event that "shit hit the fan" to use the prepper terminology, I'd prefer to be the guy with a case of antibiotics and painkillers stashed in the basement than the guy hoping I can get treatment at a hospital or local medic.
I'm not sure what the current status is, but it used to be that you could just go to a pet store and buy antibiotics intended for animal use (but hey, same drug). This is practically a prepper trope though.
If it's a cat 5 hurricane, you can fill up your tub, cooler, washing machine, rain barrel, etc. with plenty of notice. Maybe keep a few collapsed containers around for that purpose.
If you're planning for an earthquake, then bottled water makes some sense.
If you're planning for the social upheaval when the Ogallala Aquifer dries up and America's breadbasket turns to dust, then bottled water is the least of your worries - move now and settle in somewhere wet before the Okies ride again.
If you think global climate change will bring 30' snowfalls and ice storms to your area, then you'll have access to plenty of fresh water - if you have the fuel to melt it, and keep yourself warm.
Without probability estimates, apocalypse scenario planning is irrational.
Once you start talking about weeks, drinking water is easy. A relatively clean source, a big pot and a fire are all you need.
It's also easier to move around an empty several gallon pot (or just break into a house and grab one) than it is to move around hundreds of gallons of water (a short supply for several people).
(re fire, if you build a stash, you really want there to be trees around, and pretty good annual precipitation)
Any sort of real collapse is going to be accompanied by a lack of diesel and there aren't a whole lot of draft animals around, so farming is probably going to involve quite a lot of human labor.