As minecraft now uses individual texture files, many texturepacks have stopped including the old texture sheets for blocks and items. The item sheet in particular gives a nice overview of the textures and makes it much easier when editing or creating new item art. This program can allow texturepack authors to quickly create sheets to work from which can then be used to showcase the pack.
I have updated the item texture stitching file to v1.12 so pack authors display their item textures easier. It is true to the vanilla texture sheet with a few alterations to integrate the new items. ** I won't be updating the blocks texture sheet, sorry **
Just substitute this file with the default "stitched_items.txt" and stitch your textures.