Keep your mouth shut and eyes wide open, you will NOT need your entire toolbox, but bring some essentials like your knife, an extra coat, apron etc. Don't be afraid to ask questions especially if you do not understand something, often times I think people automatically can read my mind or know a technique. What I look for in a prospective employee is a good personality, and a positive attitude, where or when you went/go to school is unimportant to me. Oh and show up 10 minutes early and expect to stay later than they tell you. I know this sounds unnecessary but brush your teeth and take a shower before hand, first impressions are the most important. I have had some experiences concerning this but I will not go into detail.
When I have trails come in I usually assign them a task or tasks similar to what they will be doing when and if they get the job. I watch technique, ability to follow directions and the quality and speed of the work. I also try to suprise the trail by asking them to prepare a dessert-whatever they want and usually give them a portion size and quantity. So bring a recipe you like too, just in case.
MOST importantly I watch the whole time or have someone else watch the trail, the eyes will always be on you. I will not only debrief you after the day I will also talk to the rest of the staff who interacted with you throughout the day from the dishwashers to the exec chef. That is always the dealbreaker or dealmaker for me your interactions with the staff usually are a good indicator of what kind of employee and future manager you will be.
Sorry for sounding like a turd here but I have had 3 trails in this week alone and based on those experiences this is what I feel important, im trailed out.
good luck!!