ImageActivityItem.swift

//渡したい画像
class ImageActivityItem:NSObject,UIActivityItemSource{
    var image:UIImage?
    override init(){
        super.init()
    }
    convenience init(_ image:UIImage?){
        self.init()
        self.image = image
    }
    
    func activityViewControllerPlaceholderItem(_ activityViewController: UIActivityViewController) -> Any {
        return image ?? UIImage()
    }
    
    func activityViewController(_ activityViewController: UIActivityViewController, itemForActivityType activityType: UIActivityType?) -> Any? {
        if activityType?.rawValue == "com.burbn.instagram.shareextension"{
            //例えばここで真四角に切り取り処理をするとか。
            let ref = image!.cgImage!.cropping(to: CGRect(x:0,y:0,width:100,height:100))
            let cropImage = UIImage(cgImage: ref!, scale: self.image!.scale, orientation: image!.imageOrientation)
            return cropImage
        }
        return image
    }

}

TextActivityItem.swift

//渡したいテキスト
class TextActivityItem:NSObject,UIActivityItemSource{
    var shareText = ""
    override init(){
        super.init()
    }
    convenience init(_ text:String){
        self.init()
        self.shareText = text
    }
    
    func activityViewController(_ activityViewController: UIActivityViewController, itemForActivityType activityType: UIActivityType?) -> Any? {
        //Twitter投稿時のみハッシュタグをつける
        if activityType == .postToTwitter {
            return shareText + "#ハッシュタグ"
        }
        return shareText
    }
    
    func activityViewControllerPlaceholderItem(_ activityViewController: UIActivityViewController) -> Any {
        //ここではNSObjectを返しておく
        return NSObject()
    }
}

ViewController.swift

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let btn = UIButton(frame:CGRect(x:0,y:350,width:100,height:100))
        btn.addTarget(self, action: #selector(self.btnTapped(sender:)), for: .touchUpInside)
        btn.backgroundColor = UIColor.red
        self.view.addSubview(btn)
    }
    
    //ボタンが押されたとき
    @objc func btnTapped(sender:UIButton){
        let text = "シェアするテキスト"
        let image = UIImage(named:"image1.png")
        let activityItem:[Any] = [TextActivityItem(text),ImageActivityItem(image)]
        let activityVC = UIActivityViewController(activityItems: activityItem, applicationActivities: nil)
        self.present(activityVC, animated: true, completion: nil)
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}