Anyone know any spots to walk in on one's own and some some light casting?

Are you looking for something near town, or are you willing to drive a bit?

I've caught some fish on the Gros Ventre just south of Slide Lake, but I'm not sure what the water flow looks like right now for that area. The lake was really high in July, so it might be OK.

Pacific Creek is pretty good and accessible. The mosquitos are evil, though.

Honestly, it is so condition dependent I would go into a fly shop, ask advice on what is working, and where to go given the water temps and flow. Buy a bunch of flies and your license and the folks tend to be pretty helpful.

Flat Creek on the Elk Refuge is open. Big Cutthroats that will teach you to stay low and stealthy.