oh and in my experience, it's not the main christmas dinner where your money is going, look at all the other foods you've added. For example, it's not uncommon to have added after dinner mints, christmas biscuits, lebkuchen, mince pie, crisps, 2/3 types of nuts, twiglets, quality street etc... really, you only need one sweet snack and one savory, and if you have all that, noone will miss christmas cake... You will have food gifts over christmas and people will bring food gifts with them, which are more likely to be of the snacky variety.
soft drinks, how many options are you offering? Christmas day I'm offering wine, water or squash with the meal, coffee or tea otherwise. Boxing day my BIL is coming who loves diet coke so I'm buying in pack of cans for him, but that's it. DH will pick up some beer as well for others on boxing day.
We tend to do a buffet in the evening on Christmas day, but from experience, cheese board, cold cocktail sausages, ham sandwiches and cherry tomatoes and grapes get eaten. Stuff poeple can pick at and enough that you can make something for a toddler who didn't massively overeat at lunchtime (just because I pile up the DCs plates doesn't mean they will eat any more than at a normal lunchtime!). Then we have cake of some sort. Salad, other buffet things, don't get eaten. Or if they do, it's out of politeness as it's there.