Since it's a wedding reception at 2pm, I would buy everything at Costco. You can class it up a bit, with an early dinner.
Appetizer: cheese and crackers
Drinks: soda, water, (wine and beer optional) or just punch in a great big bowl
Food Buffet Style: 30 people - two honey spiral hams(just needs to be warmed up), Rice or mashed potato (can be made on the stove top), Salad (can be made the night before, just put tomatoes, olives and cucumbers at the bottom of the salad, toss and put dressing on the side right before serving) and rolls and butter.
Dessert: Costco sheet cake (cheap and feeds a lot of people) and sooo good.
Can't get any easier then that, keep it simple and the cost is low by buying everything at Costco.
*****Disregard my post, I went a little overboard, and somehow missed that your sister owns a cake shop. I'm in la la land today, sorry.