It’s always a little fascinating seeing the lists of skills it would be “good to know after the collapse.” I’m struck that it seems to always have the same handful of skills–all very useful, of course, but I don’t think they go far enough: sure, you’ve got advanced medical skills, but you may not have the antibiotics to go with said skills. And for “barterable skills,” they always (always) list “brewing beer.” Which is fine, but…
As a homebrewer (since before I became a prepper), let me assure you that lots of people out there brew beer. Lots. More than a few of them even brew pretty good beer. Even setting aside the notion that after a “Mad Max” collapse, any beer is better than none, your best bet for all those cans of malt extract, unless you’re a really avid homebrewer, would be to skip the beer and barter the cans.
No; where I think people would be better off focusing their time and efforts would be learning some of the earlier steps in the supply chain. If you’ve got a garden bigger than an apartment balcony, you probably have enough room to grow a little grain. Even if you don’t have enough for what they somewhat quaintly call a “pancake patch” (about 100 square feet), you can grow up a planter-full (about two square feet), save the seeds, and repeat until you have a bit of land to use. (The USDA will send US citizens 5 grams of seed of any variety, for free; 5g of wheat or barley will plant about 2 square feet. Check out their website for details.)
You could even go further back the chain: Blacksmithing would be useful to make a hoe to work the ground; basic smelting to get the metal to make the hoe. Colliery (yes, it’s a thing) to make the charcoal to smelt the metal/provide to the blacksmith to work it. Or further down the chain: You’ve got the grain, but you can’t brew with that–at least, not well. You’ve got to get it malted, or learn to do that yourself. Or milled, for bread flour. (I’ve seen plans for making a cast-concrete large-ish mill wheel; being able to save others from the drudgery of hand-cranking their grain mills for 5 minutes every time they want a loaf of bread might be worth a bit, in trade. Folks made their livings doing that until quite recently, after all.)
What other things come to mind? Paper making. Ink making. Leather tanning. Woodcutting. Sawyery/lumber-cutting. Fiber spinning, dyeing, and weaving–either plant or animal; things branch out tremendously just there. Any sort of construction or repair work. Making the tools, and knowing how to use the tools once they’re made. And let’s not forget the purely artistic–just because TSHTF doesn’t mean the world suddenly goes all grayscale, like movies from the 1920’s. Even if the item is functional, it can still look good. (Eastern European museums are full of such things; the Russians, among others, had little to do over their long winters–aside from keeping warm–so they spent their time intricately decorating even the simplest implements with some incredible carving.)
Those are just a few ideas, and I’m sitting here pretty much spitballing. There are so many different things you can learn to do. Get with your community, see who knows what, see what skills you’re lacking, and do a little research–learn the skills now, while you have the time. If nothing else, you’ve got yourself a pleasant little hobby.