Hey Laura, it's the last 3 weeks before your contest. If I were you, I wouldn't do any kind of snacking. Just stick to your diet and dig in. Don't do anything that will screw yourself up.
Well, sometimes, a "snack" pre-comp is inevitable. Often, people who have variable schedules will need an extra meal or snack built into their diet so that there is never more than 3 hrs in the day between meals.
My diet has flexibility for an extra meal if I need it (for example, if I wake up at 5am and go to bed at 2am due to my work schedule). Usually, I will start off splitting my meals in half and eating every 2 hrs rather than every 3..........but on the REALLY long, crazy days, I still need to add extra so that there is not a 5-6 hr gap without a meal. I think as a once-in-a while thing it's okay to do that--provided you limit the 'extras' to clean protein and fibrous carbs.