Heavy duty aluminum foil, a pack of half size deep steam table aluminum pans for the drip pan (get a Sam's or your restaurant supply store), plenty of paper towels, and BBQ gloves from texasbbqrub.com
I second the Thermapen not only for BBQ but for cooking in general- checking grilled chicken, roasts you may do in the oven- I even use mine to check the oil temp when I am pan/deep frying.
Enjoy your purchase- make plenty of notes to tweak for next time, trust your thermometer, and don't open the door.
I only find two things that are difficult with this smoker- What am I going to smoke and cleaning the grates but that is what the Wife is for!