Well first of all, the wizard has a little mini-quest to do. If you meet him up in the railroad area you'll get the quest. There's also a thing about building Pam a new house, but you have to be good friends with her for that. And the major postgame thing now, post 1.5 update, is Ginger Island. Eventually Willy will ask you for materials to fix up a boat he has in his backroom and that will take you to Ginger Island. I've just gotten to Ginger Island for the first time myself and at the start it's somewhat of a puzzle to figure out what you need to do. But eventually you can unlock all kinds of places and stuff on the island. You'll wanna start out by collecting Golden Walnuts to unlock stuff. Also there are various cool but expensive things you can eventually buy in the postgame, such as these permanent pillars that will warp you to the various places, so you might wanna focus on raising your profits and whatnot too, if you don't already have tons rolling in regularly.