Clean the hole and small place around the hole. Sand so you create a pit around the screw hole (Helps to hold the patch). If it is wood on the otherside take a cuetip with epoxy and coat the inside of the hole. Take epoxy and thicken (microballons are a popular choice). Patch the hole and get it smooth with a spreader to cut down on the amount of sanding. Let it set. Sand smooth and either re-gelcoat or paint.
I just filled about 50 snap holes in my restoration project. The screw holes were little so I enlarge the surface of the hole with a 1/4 drill, filled it with marine tex, sanded, then filled again with evercoat filler. Right now I'm in the priming process, and will post some pics soon