How to set up Meal Deals using a Mix & Match:
On the left of Touch Office Web: Programming > Mix & Match 2. Mix & Match 1 is not used for this use case.
There is a list of PLU slots in which you will insert all items included in the meal deal (ALL items, food, drink etc...), then you sort it by the bucket section.

If you look at the right, you can sort how many items of each bucket are needed to fill the mix & match to get the price/discount set at the top.
Other options