You can change the order of the items, especially if a field based sort doesn't give you the results you want, in the data tab - select the column(s) and move it up or down. If you have renumber items according to sort order in the options tab set the item numbers won't move with the row. It can get a little convoluted but it's doable. Ask if you need more.
It's possible the sorting function will help you. When you look at the setup of a parts list, the sorting tab can use up too three variables to sort the list.
I use: Sheet metal gage/Shape(like angles)
then the first Cut length (Cut_X, Length-manual, Frame-length)
That way the same source materials are listed together from longest to shortest
If sorting does not help, manually numbering each item is your only choice. I looked at that once a few years ago and decided to avoid any manual numbering.
One other thing that can effect the list is the sequence the parts were put together in the assembly.