The following is my list of prepper kit items that might sound good, but in practice don't really work. Avoid these items!
1) The Wire Saw (sometimes called a Commando Saw) - A small, lightweight wire saw sounds like a great idea to include in survival kits and bug-out bags. But I remember a survival show host (Les Stroud?) using one in an episode of his show, and the wire ring on one side pulled off with the first tug or two. #EpicFail
After seeing that show, I decide to test mine out. Although the wire ring didn't pull off on mine, after only cutting two small (about 1/3 inch diameter) pine branches, the wire became so bent, twisted, and kinked up that I could not cut completely through a third branch with it.
My solution: I traded up to a survival pocket chain saw. Its a chain saw blade with two nylon hand straps, and comes with a pouch that can be worn on your belt. Its too big for a Altoids survival kit, of course, but small & light enough (less than one pound) to easily carry in a bug-out bag, tackle box, or keep in the glove compartment of your vehicle. For small limbs, the wood saw on my Swiss Army Knife works very well.
2) The Emergency Fishing Kit - The problem with MOST of these kits, particularly the ones small enough to fit in an Altoids tin or similar mini-kit, is that there is not nearly enough fishing line to really be useful. Plus, the gear included in many store-bought kits are also too small and often cheap quality. There are even a couple of #FAIL videos on You Tube of folks trying unsuccessfully to fish with them. I tried out the gear I had in my old Altoids kit and had the same problem. It just didn't work. (I've since abandoned the idea of an Altoids survival kit as just a little too small to really be practical.)
My solutions: I actually have two solutions to suggest. First, I keep a Ronco Pocket Fisherman in my vehicle. You might remember the old TV commercials of the folding rod & reel with a built in tackle box? Yes, they still make them. Way too big for a mini-kit, but at only about a pound, they can be carried in or on a bug-out bag (I can clip mine securely to the back of my pack).
The second possibility is the small emergency fishing kit assembled by the folks at Survival Resources. It actually has 50 feet of of fishing line, plus other quality gear. The kit comes in something like a pill bottle which, at 3.5 inches long and 1 inch in diameter, is too big for an Altoids tin, but is still small enough to easily carry in a bug-out bag or other larger survival bag. Click here to go to their website, then scroll to the bottom of the page to find it. I'm not affiliated with them in any way, other than being a satisfied customer for several years, but tell them I sent you!
3) The Birthday Candle - Years ago, when I first got into making survival kits, I read several articles and forum posts recommending including a small birthday candle or two in your kits. The idea is that you can use a match to light the candle, which will take longer to burn, allowing you time to more successfully light your campfire with it. The problem is that birthday candles are so thin that, when you tilt them sideways to stick to the kindling, they almost instantly melt, leaving you with a hot waxy goo on your fingers and no fire!
My solution: Don't waste your time on birthday candles. You can get various types of long burning and storm proof matches to include in your kits. And I recommend that most folks include a small lighter in your EDC.
4) "Survival" Knives - You know the type I'm talking about: the ones with the hollow handles with various survival supplies inside. These tend to be absolutely horrible - cheaply made, dull blades, crappy supplies. Worse yet, they are not full tang, with the knife blade and hollow handle being held together with little more than a spot weld or two. They will not hold up to the hard use of an emergency.
My Solution: There is no need for your knife and survival kit to be the same thing. Get a good quality, full tang, sheath knife. Something like the Cold Steel Pendleton Lite Hunter might be a good and affordable option for most folks. Another, slightly more costly but still affordable, option would be the Gerber Prodigy Survival Knife. I own and like both.
5) Snare Wire - I've got two problems with the snare wire included in most survival kits. First, its too light weight to go after anything other than small rodents (the wire that came in the Bear Grylls survival kit I wrote about recently was barely more than thread). Second, there is only enough for one snare trap. Experts in trapping (and I am not one, but have spoken to several) will tell you that even if you know what you're doing, you'll be lucky to get anything more than 10% of the time. This tells me that if you really want to have a chance to eat, you need to set up several traps to increase your chances.
My solution: There are lots of spools of Vietnam-era surplus snare wire still available. It is 24-gauge wire and comes in four 40' sections on one wood spool for a total of 160'. Plenty of snare wire for many traps, and a spool is light enough (about 2.4 ounces) to easily carry in a bug-out bag. Most importantly, learn where and how to set-up snares traps before you need to depend on them.