The order may vary from flight to flight no matter how often UA tries to set a standard policy. I flew full-fare F (rack rate, no corporate discount) PDX-DEN-BOS in October, when I was a 2P only, and was offered my meal choice ahead of the 1K (possibly a GS also, I couldn't tell) sitting next to me, who politely said that I must be very important to United. On the other hand, he had bounced me out of my preassigned seat to take his favorite seat.