Like many other people, I have a favorite layer (mine happens to be body) that I almost always use to the maximum.

It would be handy to know ahead of time which items in the trunk that I am thinking about buying would clash.

You could just look it up in the wardrobe using the 'all items on subeta' option?

As said, you could use the wardrobe itself to find out. You can also look the item up on subetaHQ and it will tell you what layer each item is.

imo it's pretty easy to guess what item will be in what layer...