If you are just starting out in the fishing world, then learning a few knots is critical. I'd say I tie around a dozen knots each time I go fishing (depending on how many bluefish are around.) Often I'm tying these knots at night in a pitching boat. The ability to twist up a good knot in under a minute is very important, especially when there is a big school of striped bass under the boat.
I don't know how to tie a lot of knots because I have no need to learn them. Odds are that you probably do not need to worry about learning a ton of knots either. Having a good grasp on the following 3 knots will easily cover you in almost any fishing situation Cape Cod (and anywhere else for that matter) has to offer.