You can improvise radiator stop leak with a number of substances.
Only one time I had a reason to do that. I have a cousin who, many years ago, was proud of his 1956 Chevrolet sedan and decided to show me how fast it would go. He was doing just about all the 110 mph speedometer would register when there was a lot of banging noise up front and a small inverted dimple appeared in the hood. He very promptly kicked it in neutral and we coasted to a stop on the shoulder of the highway. We thought we'd surely blown an engine.
This was a state highway and we had seen nothing in the road that we could have hit, but in examining things under the hood, it was obvious that something had hit the cooling fins on the generator, bending one of them out quite a ways, we could see where it hit a fan blade, and it had hit under the hood hard enough to actually crack the metal. It had also knocked 3 or 4 little holes in the radiator. Since we had seen nothing we could have picked up from the road, my first assumption was that a nut or bolt had come loose and meandered around under the hook. However, we never found a single missing nut or bolt.
So, after the engine had cooled down, my cousin started it up (ran just fine), put it gear, accelerated briskly to about 60 mph, kicked it in neutral, shut off the engine, and coasted until we nearly stopped, at which time he restarted it, and did the same thing again. About 3 cycles of start, accelerate, kill engine, and coast got us to a convenience store. But it was still 30 miles to my home and car. So he went into the store and came out with a big handful of bubble gum. He was chewing vigorously with a big mouthful of bubble gum. I was laughing so hard I couldn't hardly help him, and between chomps on the bubble gum, he was saying, "Shut up, **** **, and chew."
But we plugged all the holes in the radiator with bubble gum, got to my house, removed the radiator, and took it in my car to a radiator shop. The guy there wanted to know what we used to plug the holes, and looked like he was going to cry when we told him. He said, "Do you have any idea how hard it's going to be for me to get that cleaned off so I can fix those holes?"

But he got it done.
