My Tools is the definitive add-on for any chat app.
The features in My Tools aren't strictly essential, but they are definitely interesting enough to make you happy to have them on hand. There is, for instance, a Text-to-Emoji option where you can rewrite any text using only emoji. Text Repeater will copy and paste the text you've entered as many times as you set it to, and Direct Message lets you sent messages from WhatsApp to phone numbers without having to save them as contacts.
There are various other features included as well, with perhaps the most interesting being the Status Saver, which lets you save any image or video that your contacts put in their WhatsApp status or Instagram story.