One thing to do is to bring Caroline to 2 hearts if you haven't already, then visit the sunroom at the back of the kitchen at the general store. The tea saplings you get the recipe for sells for a fair amount.
Forage on the beach and sell the corals and sea urchins (and the nautilus shells in winter)
Do the stuff on the special orders board, and the requests you find outside the general store. Cash in on rewards when you need money, not as soon as the quest is done.
If you have moss left over from the summer and fall, plant some trees, preferrably pines and oaks. Then make mushroom logs and plant them between the trees. Mushrooms grow on the logs even in winter, and chanterelles and morels are fairly profitable. If you run them through a dehydrator or a preserve jar before selling them you'll earn more.
