Hike and maybe even take in a hockey game.
Emerald Lake is one of my old standby hikes. If I can't decide on a hike, Emerald Lake is always one of my options. If I'm not feeling energetic or am short on time, Emerald Lake becomes the top option. It's a short hike, it's scenic and the lake is quite pretty.
The trailhead to Emerald Lake is on the south side of the Coldwater Creek Campground parking lot. On busy weekends you may have to park on the north side, but that shouldn't add too much distance to your hike.
The entire hike is forested. Except for the beginning of the hike, the trail is pretty straight. The beginning of the hike is the steepest, although compared to other trails in the area, the trail isn't very steep. It is just one mile from the trailhead to Emerald Lake.
Once at Emerald Lake there are some short trails that will enable you to explore the banks of the lake. The lake rests below one of the more scenic sections of the Mammoth Crest, making for some excellent views of the surrounding mountains.
An interesting fact about Emerald Lake is that when the lake freezes and there isn't much snow on the ground yet, the locals hike up to Emerald Lake and ice skate on the lake. They even play hockey on the lake. The north end of the lake is usually the last to freeze because it is the only part of the lake that gets sun during the winter months. If you're looking at the water at the north end of the lake and see what looks like perfectly round, flat rocks, they're probably hockey pucks. I've seen them play and they lose a lot of pucks that way.
Check out the Official Route and Triplogs.