Why can't I drag my items into a different order?

There is no drag handle, but there is a Sort box — on the Add item form and inside Edit on any item. Lower numbers first; equal numbers fall back to alphabetical; blank on a new item means 'put it last'. Categories have the same box on Manage categories, so category sort orders the sections and item sort orders the dishes inside them. The Excel import still works too — your sheet's row order becomes the item order.