An old catering trick - If you make a vegetable tray ahead and store it in the refrigerator, it may dry out overnight.
To keep it moist, under the plastic wrap or tray lid just lay a couple or thin layer of moist clean paper towels over the vegetables and they will look great. If needed spritz with some clean water using a spray bottle.
I just take a clean paper towel and dampen it under water and lay over the tray.
This will add moisture, you can even keep it on until the minute you serve it will keep them cool a little longer, this is due to the fact that the damp towels remain cool.