Some items will always sell better than others. If your inventory is particularly large, being able to access the biggest sellers can mean a faster sales process.
While looking at your items through Inventory Management, select the popular item, and choose Add to Favorites.
Once you've added to it, touch the Star icon at the top to access your Favorites list.
After you have a few items, you can hold down on the item and drag it to change the placement.
The position will remain even when creating tabs or shopping carts.