What about a mud cake? They are robust and you could ice them with ganash when you get there. You could do a couple - choc and white choc or caramel... I've got some recipes if you like.
Or an apple & berry crumble & take some cream & custard in an esky to have with it?
Or make a few slices - chocolate brownies, lemon slice, rocky road... and make a slice platter?