Hi Katherine,
It`s great that you are putting together this party, but you didn`t mention why press members will want to come. What`s in it for them? Are you providing entertainment, late-breaking news, a special presentation, or something else?
I hate to bring this up, but when I was working at a big PR agency previously, one of my bosses scheduled a large, press party. She had brochures, media kits, a great location and food - But no media members came to the event. It was a big loss!
You`ll need to offer some major benefits for the media. Otherwise, it could be a waste of time and effort.
Just a thought...
Melanie
I will provide food, drinks, a business presentation, and entertainment. They have to RSVP and I don`t finalize anything until I have the RSVP.
That sounds great! It sounds like you have things covered. Good job! 
Another two cents...with the event timing, you may want to offer some kind of unique "door prize" or gift that helps media members save time and money during the holiday season that is related to your various charities/theme.
Melanie
Can`t have a party without a themed drink 
At this event, we`re calling `the shots`.
The media specialty shot drink of the evening will be:
"a blankety blank" make up a name and tie into the theme. You can offer have a non alcoholic version as well.
Another thing you might want to have at the event is other VIP`s from corporate entities in the area who also support those charities and/or companies or a few individuals with inspirational stories that have resulted because of the works of those charities. Usually the charity Executive Director can tell you who those entities are. Good Luck.
Love and Laughter 
Shonika
I love Shonika`s ideas! Plus, I like the idea of a discount. You can also give out a special website address where they can go to get the discount/special products. This way, you can capture e-mail addresses and track the amount of people who actually take advantage of the discount.
Melanie
Sounds good Katherine!
Melanie