Additional items to add to carrot cake recipe

Hi Christine! You might want to look at recipes for Hummingbird Cake, such as this one from Southern Living (they call it "our most popular and beloved Southern cake recipe ever.") Pineapple is an integral part of their recipe, and they call for an 8 oz can of crushed pineapple including the juice.
https://www.southernliving.com/recipes/hummingbird-cake-recipe

Christine Lardner - your choice, but I think your changes will result in much wetter cake, maybe holding together less. Maybe tending more like a fruit nut pudding.
If (as a guess) you want reduce oil and calories and increase fruit and fiber, here are few suggestions.
Replace maximum half of the oil (3/4c in this case) from original recipe with either applesauce or pureed banana. (This works, and slightly changes the texture). Keep half of the original oil in recipe.
https://www.tasteofhome.com/article/applesauce-to-reduce-fat/
The pineapple, shredded coconut and apple additions come to about one cup volume. If you want to add them, I would omit one cup of the shredded carrots in the original recipe. This will change flavor and texture, but roughly maintain original ratios of fiber and moisture.
The additional walnuts will probably work. Most carrot cake recipes use one half to one cup nuts. If the walnuts bring the total over one cup, the cake will likely be crunchier and slightly drier in texture.