In the menus and anywhere else the weight option is given, the heavier items will sink and the lighter items will be positioned nearer the top.
Weight values are between -10 and +10. So a positive 10 is the heaviest weight while and negative 10 is the lightest weight.
Here is an example of a weighted list with the respective weights and where they would show up:
Feather -10
Apple -5
Melon -1
Bowling Ball 6
Tractor 9
If this is only somewhat clear, try playing around with different weights and see where the items after update.