One versus one drills are a good way to work on your fitness and you skills. In the video below they use a keeper, but you can just setup a small goal or two cones and have the players go at one another.
The constant action of both offense and defense will help build up ones stamina and overall fitness. Notice how the players on offense drive at the defenders, and the good defenders don’t dive in but hold their ground.
Ensure you have an arsenal of skills to dribble past any defender thanks to this @CoerverUK soccer drill: