Simple Item Collector Test + Release with Button

CollectItems.cs

using UnityEngine;
using System.Collections;

// attach this script to your player gameobject
// player needs RigidBody2D and some 2D collider
// your collectible objects need: 2D Collider with [x] Trigger and gameobject tag: "Item"

public class CollectItems : MonoBehaviour
{
    public float speed = 10;
    public Transform carryLocation; // this is empty gameobject as a child of player, object will be carried on this position
    Transform currentItem = null;

    void Start()
    {

    }

    void Update()
    {
        // basic movement
        var x = Input.GetAxis("Horizontal")*speed*Time.deltaTime;
        var y = Input.GetAxis("Vertical")* speed *Time.deltaTime;
        transform.Translate(x, y, 0);

        // press fire to drop item, if carrying something
        if (Input.GetButtonDown("Fire1"))
        {
            if (currentItem!=null)
            {
                // remove as child
                currentItem.parent = null;

                //set position near player
                currentItem.position = transform.GetComponent<SpriteRenderer>().bounds.max;

                // release reference
                currentItem = null;
            }
        }
    }

    void OnTriggerEnter2D(Collider2D other)
    {
        // pickup if it has tag "Item" and we are not carrying anything
        if (other.CompareTag("Item") && currentItem == null)
        {
            // take reference to that collided object
            currentItem = other.transform;

            // move it to carrying point
            currentItem.position = carryLocation.position;

            // make it as a child of player, so it moves along with player
            currentItem.parent = transform;
        }
    }
}