Mouth rinse for sores and/or canker sore medicine.
		
		
	 
This. It's found in the toothpaste section of a department store.
I've found Orajel to give a bit less of an "OH GOD IT BURNS" feeling upon application than Anbesol.
I usually use the "toothache" formula. The officially-labeled "canker sore" formulations have some goo-forming agents in them that allegedly help protect the sore. All I've found them to be good at is forming goo, and not much else.
The store brand usually does the job as well as the expensive name-brand 
Also, be sure to get something that has 20% benzocaine. There are weaker formulations with 10% or less.
I've gotten those things constantly ever since gradeschool. Going through braces in high school was awful - most of the inside of my mouth turned into a nasty irritated sore spot, on top of the constant headaches from having my jaw forcibly reconfigured. 
I'd have bought pure benzocaine by the barrel if I could have.