I use a small, relatively deep, corelle bowl or a custard cup depending on how much extra I add. I put a small amount of chopped onion, some herbs, a few bacon bits and some chopped mini pepper in the bottom of the dish and top it off with a whisked up egg and nuke it. I have used all sorts of things, including asparagus and mushrooms. I have used a bit of crumbled MorningStar sausage. Most recently I put a bit of shredded up spinach in the bowl. I nuked it just a tiny bit before I added the egg.
I make up my container of egg and extras and cover it tightly with food wrap. That way, I can carry it in my lunch bag and when it is time for breakfast just peel back the wrap a bit and nuke it.
Diced ham or any other lunchmeat you prefer is another good addition. I love pepperjack, ham and spinach (definitely agree with nuking it a bit first before adding the eggs.) Onions, crumbled bacon and bell peppers are another good choice.
I should try putting in mushrooms and smoked swiss cheese, I bet that would be so good!