Try doing a superset before your walk. For example, try a superset of squats followed by military press 3x, then go walking.
For those of you who don’t know what a superset is, it is doing one exercise immediately followed by another exercise without any rest in between.
So in this case you would do 10 reps of squats followed by 10 reps of military presses. Then rest and repeat the exercise two more times for a total of 3 sets.
When your done, hit the pavement and start walking.
Experiment with different exercises but I would highly recommend supersetting a lower body exercise with an upper body exercise.