Nest the smaller bowl, dish, vase, or container within the trifle dish, which should leave a 1.5"-2" gap between the two dishes.
Pack Easter grass in this gap until it fills the bottom ⅓ of the trifle dish. You'll likely have to poke it with scissors or a long skewer to get it to lay the way you want it and to create the appearance of an even layer. Make sure you use a generous amount of grass so the M&Ms do not immediately fall into any gaps.
Now, pour the M&Ms into the gap to create an even layer on top of the Easter grass. Again you may need to move some of the candies around to create the appearance of a perfectly even layer.
Now it's time for the Peeps! Add the Peeps bunnies to the very top of the trifle dish--they can even stick out a little bit (which might help hide the inner dish). I use two 8-packs of pink Peeps bunnies, but the number needed may differ depending on your specific trifle dish.
Arrange your flowers in the smaller container in the center. Depending on the size dishes you are using, it may be helpful to nest an even smaller jar or container in the very middle of the centerpiece to make sure the flowers sit nicely and don't flop over. Or, you may find floral foam helpful in arranging the flowers.
Add this centerpiece to your Easter table and enjoy! When adding water to the container holding the flowers, be careful to not pour any within the gap holding the Easter grass and candy. It can make the candies bleed color and make quite a sticky mess (speaking from experience).