Not just online orders, but all orders, under kitchen, kitchen setup, you would have to turn item sorting priority to by sort order. Then under advanced properties, check sort order under preparation and assign numbers to menu items (lower numbers appear higher, identical numbers appear together)
You can just give the same number to every item in a menu group or you can get very particular with it, I personally give each item a unique number so that they appear together on a ticket when multiple of the same item are ordered. Can be a little difficult to manage if you change menus a lot though. It helps to plan ahead and come up with some sort of system, I give blocks of numbers to each group so that there is room to easily add items in the future without having to redo the whole menu, like 20-39 for sandwiches for example, 40-59 for salads etc.
