There’s a track (Lairig Ghallabhraich) from Carie on the south side of the loch over to Glen Lyon, refreshments at Bridge of Balgie tearoom :-)
Return the same way or make a loop by going down Glen Lyon, Coshieville and the Shiehallion road.
From Kinloch Rannoch by road to Trinafour and A9 cycle path. At Dalnaspidal go down Loch Garry then carry on south to Loch Rannoch. The middle from the end of Loch Garry to Duinish can be boggy!