If you've ever had your leash plug ripped out in powerful surf, you learn pretty quickly that not having a board to rely on to get back in can be stressful/scary.
All of us as surfers take our leash for granted most of the time, and appreciate it most when you need it most...When it's pumping on the outer sand bar or reef.
With some useful home materials, you can become your own repair shop with a little resin and technique.
Tape off the bottom side of the exposed part of the plug, so that we can add resin from the top of the board.
Mix Epoxy and Hardener, and then add the Filler (You can buy this repair kit here)
Fill empty plug hole all the way with your filler mix, and then drop the plug into the filler. It's perfectly fine if extra filler overflows onto the deck of the board, you're going to end up sanding anyway.