Can you assemble onsite?Or not depending on how long from production to presentation. I found these will hold up at least a day in the walk-in:
Napoleons using puff pastry and pastry cream. Pastry cream is one of the most versatile things on the pastry planet. You can flavor it any way you like. Mix it with stabilized whipped cream for a Bavarian Cream effect.
Chocolate and a ganache topping is nice, or vanilla and a standard glaze/chocolate ribbon deco. You can also cut them in any size you like from a petit four to a brick.
Bake the pastry up and make the cream in advance and slap it all together last minute. Yummy, easy, and popular.
You can also sandwich fresh berries in the cream.
Another idea would be to blind bake mini shortbread tart shells (I use mini muffin tins) and fill with pastry cream. Top with fresh berries, glazes, whipped cream (also stabilized) They also have a long shelf life (in the cooler)
You can mix Pastry Cream with different liquors, make a creme de menthe, grand mariner, irish cream...you name it.