I'm assuming you mean in the week before leaving for nationals. I never had any specific activity that I did in this time; I really just crammed as many words as I could into my head. However, one important thing to think about is the psychological aspect--your chances in the bee are better if you've found a way to make yourself more confident. My former coach, Scott Isaacs, told me to make a playlist of songs that helped increase my confidence and excitement for the bee. That really helped me, but each person is different, so there could be any number of ways to do this.
Once spellers get to the bee, there are a few days before the competition actually begins in which Scripps holds a barbecue for the spellers and a few other activities. I recommend going to all of these if possible--even if you want to study, it makes a nice break from studying as well as creating an opportunity to meet other spellers.
Hope this helps!