I got a mini crock pot which is pretty popular at our station (and it's super cheap). It does take 45-60 min to heat your food fully, but I just plug it in and forget about it. It has a standard wall plug, but we have a power strip in the back with a long enough cord to reach the front. Its not very big, but it works great for leftovers and soups!

20 oz: https://www.amazon.com/dp/B00CEILWI0/ref=cm_sw_r_cp_apa_nF9XAbWJ1HDVN

24 oz: https://www.amazon.com/dp/B00H70KP8I/ref=cm_sw_r_cp_apa_7D9XAb3YASQJ7