all backpack files are not broken.
You need to edit ".ifl" file...
(acc_backpack_low.ifl, acc_backpack_lrg.ifl, acc_backpack_smll.ifl)
Open the *.ifl file with text editor (eg NotePad)
Put the texture file (.tga) you want at the top of the line.

It's just simply that.
attached GameStudio MDL7 files.

Have Fun!