If you're into that sort of thing, cutting a christmas tree up in the mountains is a nice outting. We cut ours in Sinks Canyon in Lander that year, and I enjoy looking back on the video we took of my daughter and cousin sliding on the snowy/icy road.
Other ideas: Ice skating, sledding (yeah, I know, no snow atm), library trips (we used to rent videos at the library as well as books), and I found this
calendar of events for Riverton on the chamber of commerce website that showed what was going on now. Festival of trees is mentioned, as well as sporting events. Good luck!