Have combo box(es) with a list of items plus the All option update the row source of the list box as an item is selected from the combo box. Have the ability to sort the combo box and also ignore items no longer available. Is it possible to select more than one item in the combo box like it is in a listbox?

Combo boxes and list boxes are very similar, but they do have some major differences. For example, there is no such thing as a multi-select COMBO box. You can only pick one item. However a combo box does give you the ability to type in your own values (if you choose to allow that). And ALL ALL option might be nice for the food options list box, however if we have things like "cook medium" and "cook well done" on there, it might be pointless. I'll think about that one. List box sorting is easy and we'll cover that. Items no longer available will definitely be covered (I mentioned that in D14). You've got my Search Seminar. Some of this was covered in that.

Indicate when a selection returns no results, there could be multiple items that have no sub items so clicking you don't know if it worked or there was an error.
This could be a "No items found" or change the colour, or toggle a label.