How much cardio are you talking?

Just remember that you have to recover from cardio like anything else, and that cardio (in an evolutionary perspective) has different body mass requirements than weight lifting. So I would pick cardio that was under load (like your typical sled drag, or even walking on a treadmill while carrying weights) or make it short duration high intensity (sprints are good, hill sprints are better). and there is always fun stuff like this!