I want to provide roasted broccoli, carrots and onions for a lunch pot luck. I will have access to an oven but do not want to make a big production of on-site cooking. I want to avoid dealing with numerous large pans. I was thinking of doing the carrots and onions in advance and then doing broccoli just before lunch and adding the other items at end to heat thru. Would it be better to cook carrots and onions in AM and hold at room temperature rather than cook night before and have to refrigerate?