Matching the finish is pretty hard. The varnish
on most teak
ages with a patina that you just can't match easily. You might do as well with a little mixing using a Minwax stain finish. If you had the inside of a cabinet or some place unseen you could do some experiments. Maybe get pretty close too.
Done well it would have been over drilled then plugged with a spot of glue in the hole. You can buy 3/8 or 1/4 inch teak plugs (West Marine), drill out the holes and at least have real teak wood. You need a good drill bit and drill it straight. You can even get fancy and line up the grain of the plugs. You need to sand them down though and that makes a bigger area. It you sanded the plug
flat and smooth (they don't come that way) you might get it by tapping them in (don't go too deep). The finish you might try to match on a scrap piece of wood and stain some plugs to see how close you get. It would be better than plastic wood and pretty easy.
The fiddle is different. You won't use plastic wood to make that look anything but worse. Sanding
it smooth and trying to match the finish would look like a well earned war wound fixed by someone that cared. It may be as good as you need. Anything you try to patch it with will look terrible and won't hold. Make it at least safe and then maybe save it for a time when you feel like replacing the whole fiddle.
You really don't want to eat and look at a band aid for the rest of the time you own the boat. It's one of those do no harm jobs.