Re: Flare-guns and other alternatives (excluding guns) as weapons
Wasp spray is NOT a serious weapon. The notion that it is, is nothing more than an urban legend. I've been sprayed with wasp spray before, accidentally. It did not even come CLOSE to incapacitating me.
If you don't want to carry a gun, for whatever reason, my advice would be a squirt bottle full of amonia. To customs it is just a cleanser. Give someone a squirt of that in the face, though, and they are going to be in a world of hurt.
Some fishing sinkers in a sock can also work pretty well. Have that in one hand, and the amonia in the other, and I think you would be about as well armed as you are going to get, without opting for a real firearm.