A couple people have suggested power tools ... I'll add that whatever battery platform you wind up going with (I went with Ryobi ... good enough for my purposes), also pick up an adapter that'll use the battery and give you AC power as well. Having an adapter that'll power anything up to 150W has been a godsend.
I've also got a bunch of flashlights/lanterns that use the same batteries ... super convenient if we lose power and it's great when we go camping too.
I've got a "battery charging station" that's just a plastic shelf, when you come in from the garage and it's got the Ryobi batteries charging, but also our USB charging packs, rechargable AA/AAA/etc... batteries, and it's also where we keep a lot of the tools so it makes it easy to find things in an emergency.
-=-=-=- If your house has a sump pump but no battery backup (and I'd actually recommend the ones that are FULL replacements ... so, you'll basically have two pumps in the sump, one of which is connected to the battery system), I'd definitely recommend you getting one before you need it.
-=-=-=- For myself, my AC unit has two capacitors. One burned up the first weekend we were in the house and one burned out a couple of years later.
The first one, I didn't know anything at the time and it cost a bit more than $600 (we thought we were getting screwed [and we were], but, it was 110deg F with fans running, so, we weren't in a position to argue and the tech knew it). It's a $20 part if you just buy it online and many times it will physically deform when it breaks, so even with no knowledge you might even have a physical indication that it's broken. Go to your AC unit, give it a thorough cleaning (youtube the process) and then look up what capacitors your unit uses and buy a spare set and watch a quick video on how to replace them ... super easy. It's likely you'll pay < $40 for however many you need and you won't have to deal with a massive bill for a $20 part that you've just got to match up the ports and then move the blade terminals from one to the other AND you won't have to deal with a hot house while you wait for a replacement since you'll already have one and you'll just have to buy a replacement for your spare, but, even if that takes a month to ship, it won't be a worry.
-=-=-=- A GOOD tape measurer. I've got a great Milwaukee one that has a magnet on the tip and it also holds without bending for a decent distance and it's been glorious ... always sucks when you're trying to measure something and the tape is just flopping around not able to hold its shape.
-=-=-=- There are a lot of studfinders out there, but I've found the ones that work the best basically just have a magnet that finds the nails/screws that are holding the drywall on. Once you've found a nail, you've found the stud.
It's right there in the name, trade SECRETS.
Those are kept safe by legal agreements compelling secrecy, not letting most people know the secrets and other methods, but, if the secrets got out, the person who leaked it might get in trouble for breaking a legal contract or breaking and entering or whatever, but, the rest of the world would be able to legally sell things made using those recipes, but they probably wouldn't be able to reference the original company directly (ie, Crowns Chicken, now using KFCs original recipe!) ... "11 herbs and spices" is probably a term that's trademarked too, but I'm sure some marketing person would find a creative way to tell everyone.