My go to easy dessert is chocolate meringues with freshly whipped cream. Easy, quick and I confess, inexpensive to make. Easy to transport if you need. The meringues themselves are easy to store for long periods of time. No refrigeration required.
If you want more cake like - I always make a chocolate torte. Pillsbury have a great recipe. Making it today for Sunday I would imagine would be just fine. I have always done day before.
http://www.pillsbury.com/recipes/milleniyum-chocolate-torte/60d0ecd7-d204-4592-a008-4975c1472492/