Say that you've decided to transfer a whole bunch of items from a previous fort to a new location via Pack Muleventurer.
You can make things easier with the following tips.
1. Items that are left in a workshop when you abandon will remain there.
2. Don't sleep as items will scatter again.
3. Artifacts can only be removed from the site if they are placed in a bin and the bin itself is carried. You can remove a copy of the item from the bin that will disappear the instant it leaves your hands and can duplicate items via this process.
4. To avoid having that bin randomly move across the map, you can put it in a room behind a locked door and it will remain there.
5. Now, say that you have a nice lair picked out to put all of these recovered goodies in. Make sure that you are well away from the door/ramp as items placed there will still scatter while objects inside the lair will not. So you've spent all that time lugging an entire abandoned fort's worth of items halfway across the world map. That's all well and good, but now you have to empty that humongous backpack one item at a time, right?
Nah, here's what you do. Get a waterskin and fill it with a liquid; water is best, but this will work with other things. When you get inside of the lair, pick out a location for where you want to create a quantum stockpile of your items. Walk over there and hit 'd'. Select the water/liquid in the waterskin, which will empty the entire waterskin. Now, hit 'g' and pick up the water that you just dropped. Make sure that it goes in your backpack and that you didn't have an empty hand for some reason as the water will still be in your hand. If it does, just use 'p' to put it in the backpack. For the record, you can pick up an infinite number of handfuls of water as puddles created by waterskins are apparently the same as aquifers in adventure mode. If you get stuck in the mountains with nothing to pick up and throw, you can do this and flatten a kobold's skull with a handful of water. You can also use this trick to have one waterskin refill fifty if need be, but killing kobolds with it is a lot more fun.
Anyway, so you have your handful of water from that infinite puddle in your backpack, right? Hit 'd' and select the water that is in your backback. The game will decide that your backpack is now a waterskin and will mass dump everything at once. Now you can go back to hiking through the world, kicking monsters to death, or waltz back to the nearest city of your home civ so that said adventurer can show up in that fort and enjoy the fruits of his/her labors.