The Misty Satchel is a free 34 slot bag (unique) available in the Dragon Isles. It drops from the Misty Treasure Chest in the Crumbling Life Archway in The Waking Shores. While sitting in the "cave" coordinates reads 58, 53.
It is in a cave behind a waterfall. (Some say it is not a cave but it is a room in the rock that's close enough) The cave is close to the top of the falls. Which means you have to have to be able to fly. Or You can use a goblin glider from the top of the falls.
If you can fly, see the pic "Looking at Waterfall". Fly in just above and to the right of the rock sticking out from the falls.
The Evoker video shows him flying in.
There is supposed to be "climbing gear" near the falls to enable you to climb on some special rocks (including the one sticking out from the falls) but I couldn't find it. And without it you can't drop down onto it from the top of the falls - I tried multiple times and went right through the rock. - If you do find the "climbing gear "See our pic "climbable rocks" with the rocks in question marked.
There are links on the left side of this page to some images and videos.
There is an image of The Waking Shores map with the bridge by the falls marked.
Another of my character on the bridge looking at the falls.
The Evoker video shows an Evoker going to the flight path by the boat landing. Using a ground mount to get to the bridge by the falls and then using soar to fly through the falls.
The Warlock video shows a warlock flying to the Ruby Life Pools and using a goblin glider to get to the top of the falls. Then a goblin glider to fly into the cave.
The Paladin video shows a paladin running from the base of the falls to the top of the falls and making 4 attempts before finally goblin gliding into the cave
The Misty Satchel in 3 minutes video shows a priest starting in the SW Portal room, porting to Valdrakken, flying to the Ruby Life Pools and then using a dragon mount to fly from there into the cave (all of which takes like 2 min 30 sec)
(All of my toons that went to the Dragon Isles for the first time via the portal in Stormwind were given the Dragonscale Basecamp flight path automatically)