I like to bake some side dishes in the pan with the meatloaf, almost like a pot roast, so they give each other flavor. I would suggest quartered potatoes with the skin on, carrots, and onions (leave small or medium onions whole; quarter large onions). You can either mix all of these together and serve them as a single dish, or have three different rows in the pan so that you can easily scoop them out as three different sidedishes. Whether mixed or separate, put a layer of vegetables at the bottom of the pan, then put the meatloaf on top of it and bake.
By the way, if you were already planning on mashed potatoes, it's okay to have these potatoes, too. They are different enough to be a separate dish.
I also like to have cottage cheese with meatloaf.