Re: Spur of the Moment Trip, Mt.-Id.-Wy. Tips needed...
Hidden and Golden trout lakes up Portal Creek are pretty easy hikes.
It's been years but they were pretty easy to catch back in the day.
It's not legal to specifically target bull trout anywhere in Montana except the South Fork of the Flathead which is a LONG haul from Bozeman. At least 7 hours, probably more like 8 or 9 though you can catch plenty of Westslope cutties up there as well.
You'd be better off on the N. Fork of the Clearwater, that's still about 6 hours from Bozeman.
Lakers near Bozeman? The only thing that comes to mind is Yellowstone lake but good luck on that one. Shoshone lake, Heart lake and Lewis lake have lake trout as well but It's going to take a boat or packing in a float tube and good luck getting deep enough, with a fly rod anyways.
Flathead lake is a long ways away. Elk Lake down by Red Rocks has some as well but fishing for lakers here would be kind of a waste of time given all the other awesome fishing available.