I done Christmas in July numerous times both at my house and in my previous work (Activities Coordinator in aged care). I don't cook turkey, but I have made a plum pudding. I usually get some friends to bring drinks, shortbread, nibbles. I decorate the table only....I don't bother with the tree and the rest of the decorations because that's for the "real deal" (plus it takes too long! LOL)
I usually cook a nice leg of lamb (or pork) with roast vegies, and you can buy ham if you wish. If you don't fancy cooking a plum pudding you can buy some in a tin (dark blue) in the supermarket however if you don't feel it's too cold an ice cream plum pudding is nice (although leave the choc bits out as they are really hard when frozen. OUCH!) Or just serve coffee and other nibbles....like the shortbread, fruit cake, or make some White Christmas or chocolate royal plum puddings. Hmmm.....not really the thing for weight loss though!
I have also been soooooo prepared that I've bought cheap bon bons after Christmas and used those on the table. Red, green or Chrissy tablecloth, a bit of tinsel and Voila!