Yes, you can make the tray the day before. Leave any non-vegetable items off the tray (such as naan, pretzels, etc.), then wrap the tray tightly in plastic wrap and store in the fridge. Add the remaining items before serving. You can also prep all the veggies and store them in an air-tight container in the fridge for 1-2 days, then arrange the platter a few hours before serving.