An ability -- perhaps a skill that needs to be learned first -- to designate certain bags for certain things, like food, meals, rocks, Musicboxes, etc.
Well, right now you can name bags, and you've got bags, tool boxes, spice boxes, elemental pouches and alchemical kits. So, you're asking for further categorization? Can't complain about that!
@Carl: I think the OP was referring to an idea mentioned elsewhere and earlier for "tunable" bags, ie, meat automatically goes here; milk goes there, gems and ingots go to another location, and so forth.
Agree with AC2K that a lockable bag would also be useful.
Here's a further suggestion (related to another suggestion I made) of how it could work:
1) take an empty bag
2) add 1 item (or a stack of the same items) to it
3) use new verb: Classify (or w/e)
4) now only that type of item can be added
5) the bag includes the icon of that item type
This means that Tiny Speck wouldn't need to add more type-specific bags, because people could create their own. It also makes the bags easier to organize in a cabinet or on the ground because they have an icon of the content.
Here's what I do to work around that situation.
I take whatever I want to stay into a certain bag, drop only one of whatever that item is, and then drag that item into a new slot of the bag. You can do that for all the slots of a bag, ie. making 12 slots of just one piece of meat, and from then on, any meat that you collect, will just stack onto those meats in the bag, rather than just going into whatever bag they'll fit in.
@Bamboozler I am totally pinching that idea - why didn't I think of that? Dur! The only downside is having to spread your single items out again when you use stuff up but it's still an improvement over default behaviour...