While a mylar wrapper is pretty tough when you try to tear it, they don't do so well with pointy things penetrating it, so I would not use a mylar wrapper or a plastic bill, or other cash made of fabrics, or an old spent tube, etc.; cutting something plastic like a milk jug the edges could rub a hole into the tube as you ride. The Park boot is quite tough, but any boot is strictly an emergency get you someplace to get it fixed type of deal, even the Park boot, which is tough, it's also self sticking and that self sticking only lasts about 2 days then the boot will begin to move...just as any loose boot you created out of whatever will do. And if you are touring you shouldn't be just running on your two main tires and a tire boot for emergencies, you should be carrying a spare tire for those occasions when you have a major issue with a tire. Not saying not to carry a boot, no, carry a boot, but carry a spare tire because that will work a lot better than a boot, and a folding tire can pack quite small but I use steel beaded tires and I have a lighter tire I use for a spare that is steel beaded as well that I folded into a smaller circle and it's attached to the outside of one of my panniers.
As far as tools or repair items goes, what I pack on when I tour is similar to what most people pack.
Spare tire.
two spare tubes.
Park Tire boot
Park glueless patches (I know what some of you think of these but I know how to make them last the life of the tube)
2 Soma Steel Core tire levers
VAR tire lever
1 frame pump, and 1 mini pump for backup
Presta to Schrader converter (I make sure I can get air!)
4 FiberFix spokes (some bikes have spoke holders on the frame, if you have those then carry regular spokes)
Park MTB3 mini tool
cheap small folding pliers
pedal tool
couple of spare chain links
a nylon scrubber, actually two, one for dishes and one for chain cleaning
on the above note I carry biodegradable soap and I use that to clean the chain if needed.
several reusable medium size zip ties
3 feet of black Gorilla tape wrapped around a pencil
lube
hand wipes (I hate gloves, I like to feel what I'm doing)
small bungee cords
spare screws for cleats, racks, bottle cages, fenders, etc.
I do carry some tools for camping like a peg hammer that I could use to beat my bike with it I needed to, and I have a really strong and sharp knife that I could use for something on the bike if needed. I use a fishing rod as a flag pole so it serves double duty. I also carry a S&W 357 mag revolver, but since I don't carry a concealed weapon permit for every state I be in (I do have a concealed permit but not all states recognize other states concealed permits) I keep it unloaded and the bullets in a speed loader in another separate bag (meaning the gun is the handlebar bag and the speed loader is in a pannier, this is the only way it will be considered legal, if both the ammo and the gun are in the same bag many states consider that loaded even if it's not physically loaded), and that is legal from what I've read, when it becomes illegal is if the gun is loaded and concealed; I have no delusions about getting the gun out in time to shoot someone as I'm riding, I read where people think they can, but in reality by the time you know you're being threatened by a motorist it's too late to retrieve the gun even if you don't have to load it; no my gun is for wild animals when I'm camping, those are more of threat than another person is actually. I only carry 6 rounds and no more because ammo is heavy, and if I need more than that I'm probably dead anyways! LOL!!! While a 357 revolver is heavier than smaller pea shooters, those smaller pea shooters may not even stop a raccoon not alone something larger which all it will do is piss off the animal that will come after you, 357 is the smallest load to stop a medium size animal, some claim a 357 can take down a bear...well I don't know, black bear maybe, a grizzly probably not, but I hope to never find out. The reason I put the gun in the handlebar bag is because if I stop at some store or restaurant I can quickly unclip the bag, clip on the shoulder straps, and take it with me much easier than a pannier bag.
I did read here someone took dental floss and a sewing needle...I like that idea and I'll be carrying that too from now on.
I can't see the need for a cassette breaker, or in my case a freewheel breaker, because if I have to do that I still have to walk someplace and buy another freewheel, might as well just let the bike shop fix it since I would have to go there anyways. I also don't see the need to carry around brake blocks since I would be pre tripping my bike before each start of the day I would notice any wear and would eventually make it to a bike shop to replace the blocks.
Of course I carry cash and my card, ID and insurance cards, cell phone, spare bats for the computer, a battery that can be used to charge my phone if needed, flashlights, several different ways to start fire (always good to have the ability to start a fire, and it's always good to have a couple of back up ways to start a fire in case the first way fails), first aid kit, emergency blanket. Ok my minds gone numb, I'm sure i'm forgetting some stuff but I'm too lazy today to go get my bag and pour it all out and start listing it all, so this will have to do. Keep in mind that a lot of this stuff doesn't take that much room, in fact all of this stuff that i mentioned above which I reduce when not touring is this:
1 spare tube.
Park Tire boot
Park glueless patches
2 Soma Steel Core tire levers
QuikStik (I don't take this when I tour, doesn't work real well with steel beaded tires)
1 mini pump
Presta to Schrader converter
Park MTB3 mini tool
cheap small folding pliers
hand wipes
money
spare battery for bike computer
cell phone
All of that stuff fits into my seat bag except for the mini pump! And i still have room in the bag left for food, so while it seems like a lot it's not. Oh, I leave the gun at home when I'm not touring.