Good news! Later just released an emoji keyboard that you can access while writing your captions!
When you schedule a post, you will now see an emoji button in the top right corner of the caption field:
Once you open the emoji keyboard, you can scroll through the emojis by category or skin tone:
Or you can use the search bar to find the perfect emoji for your post:
Once you find the right emoji, just click on it to add it to your post!