I picked up a used bike a few weeks ago. The back V brake boot was cracked and looking tired. Dug out my box of assorted shrink fit tubing. Pulled the old boot. Cut a piece of tubing and slid it over the cracked portion of the boot. Then slide it back over the cable and used a lighter to shrink it up. One day I'll buy a heat gun but somehow I've survived without one.
Here are a couple pics
Sorry if this has been posted before. So many tips here. I've barely made a dent in reading them.