How strange. I just confirmed that I can split the stacks from holding shift.
Perhaps we aren't doing the same thing. I open the Traveler's Chest, open Inventory using the "I" key (opening group inventory), hold left Shift, click on the Camping Supplies and hold, drag to whichever character I want, the split menu comes up and I select 1 Camping Supply.
I had 8 Camping Supplies in my chest in the camp and was able to just take 1 out when I wanted to long rest, each time.
Now if they'd just make it so we could select multiple inventory items at once, that'd be awesome so I don't have to right click on each individual food item I pick up and select Send to Camp. Here's a suggestion. Right click on any type of item. There is an option that says, "Select All of Type". I click on that option, all of that particular type are selected. So, if I want to move all books into a backpack, I can right click on any book, Select All of Type, drag and drop book in the backpack. If I want to select all Camping Supplies and send to camp, right click on a food item, Select All of Type, right click again, Send to Camp.
