Here is a simple script I’ve added to my pickup Sword (can be added to any object) that moves the object up and down + 360degrees rotation based on a random value from a Min/Max. It was based on the “Mathf.Sin() For Oscillation” lesson from Complete C# Unity Game Developer 3D - Project Boost with a bit of simplification + random values from me 
Why I like this approach: the distance / rotation / time values are all randomly calculated in start. This gives each object a “unique” feel. Here’s how it looks in action
I would be interested to know if this sort of code would be problematic on multiple objects since it uses the Update to “animate” them. If you know of a better/easier way to achieve this, please share 
.
I’ve created a new namespace for the script called “RPG.Pickups” - This is optional
namespace RPG.Pickups
{
public class pickupFloatingRotationAnimation : MonoBehaviour
{
private float originalY;
[SerializeField] private float distanceMin = 5f;
[SerializeField] private float distanceMax = 20f;
private float randomFloat;
[SerializeField] private float timeMin = 5f;
[SerializeField] private float timeMax = 20f;
private float randomTime;
[SerializeField] private float rotationMin = 5f;
[SerializeField] private float rotationMax = 20f;
private float randomRotation;
void Start()
{
this.originalY = this.transform.position.y;
randomFloat = Random.Range(distanceMin, distanceMax);
randomTime = Random.Range(timeMin, timeMax);
randomRotation = Random.Range(rotationMin, rotationMax);
}
void Update()
{
//We Rotate the Object here
gameObject.transform.Rotate(new Vector3(0f, randomRotation, 0f) * Time.deltaTime);
//We Move the Object here - The distance and time is random for each object
gameObject.transform.position = new Vector3(transform.position.x,
originalY + (Mathf.Sin(randomTime + Time.time) * randomFloat), transform.position.z);
}
}
}