A big tray of roasted veg is easy to do - peppers, aubergine, red peppers, par boiled small potatoes, garlic, olive oil. Bung in the over 25 mins before serving.
Also Brussels sprouts with bacon lardons (par boil the sprouts and fry with the bacon). That's a dish you'd have to stand over admittedly.
Could you maybe to a potato gratin the night before, chill in the fridge and heat it up on the day?