Advance prep for BBQ?

Yes! Ina Garten's Sour Cream Cornbread from her Make It Ahead Cookbook, I have the book and found the recipe online. It's delicious with BBQ. http://www.glamour.com/story/cook-ahead-of-time-ina-gartens

From my experience I'll share what I used to do. First for desserts I would use 9 x 13 pans and make brownies or layer bars something you could cut up and share. Costco became a really good friend. Love the bags of dinner rolls from the bakery you can also get pretzel rolls.
And purchase big containers of their potato salad or macaroni salad. Place them in big bowls and add your touch of fresh herbs or paprika. Pull out the slow cooker and make baked beans. It holds a lot and feeds a crowd. Simple recipe is starting off with canned baked beans and add more bacon and spices. Many recipes online that available. Celery and carrots can be cut up a couple days ahead of time wrapped in damp paper towels and put in Ziploc bags. Simple dips like hummus or sour cream based are quick and easy. And, a big bowl of Kettle chips is always a hit with kids and adults. Good luck! BB

Sorry, no to the freezing of cornbread or muffins. They (including hush puppies) taste divine when freshly baked or fried, but in my experience taste flat and boring from the freezer.
White bread. Freeze either the once-risen dough or baked loaves. Then remove the first, do 2nd rise and bake or just remove, thaw & optionally reheat the last.
Opinion on frozen pies is divided. You pays your money, you takes your choice.
I would suggest fruit crisp for dessert, partially made, frozen, then finished day-before or day-of party. Gild the lily with ice cream on top. See, for example, serious eats on this:
http://www.seriouseats.com/talk/2012/07/freezing-fruit-crisps.html
Depending on where you are from or what style BBQ you are making, consider....baked beans, french fries from Kansas City; vinegar sauce from North Carolina; cole slaw from everywhere.

Your decision making should be guided by your skills, your available time, and your available resources, things like equipment/material, storage facilities, kitchen help, etc. Those are factors that no one here knows about, so it is very difficult to give advice like dishes or recipes.

Closely managed, I think a standard household refrigerator/freezer combo in a decenly-equipped kitchen is adequate to prep a party of 8-12 people.

Hosting a party for 45 is a completely different scenario.

Take one dish as an example. Let's say you want to serve salad and figure a medium head of lettuce is adequate for four people. That means you need 11 heads of lettuce. Where are going to put those? Do you have mixing bowls for that?

If you have never hosted a party of this size, I suggest you consider getting most of the food items from the deli counter and focus on something that is still within your range, like one or two sets of cookies. You should also look at focusing on beverages.

I don't know whom your audience is, but just organizing a full bar plus beer, wine and juices/sodas for kids is already a not insignificant amount of effort. Are you going to brew your own coffee and tea for 45?

Anyhow, perhaps others here will have different things to share.

Good luck.