My great grandma's banana bread tastes great, but I want it to be moister and denser. What do I add or change?

Sub out some of the butter for oil. I used to make a banana bread with all oil, and it was delicious, dense and moist.

I wonder what effect some banana pudding mix would have? A tablespoon or so?

If there are already 2 - 3 eggs, I find that omitting an egg will help it be moister. And make sure the bananas are so ripe that they're black! (But it's true that the existing recipe is really the first thing to consider here. It might need less flour, more banana, etc., depending on current ratios.)

Add a 1/4-1/2 cup of applesauce with the wet ingredients portion of your recipe.

Vegetable oil will make cakes moister and denser. What fat are you using in your recipe?

Oops -- that comment was meant to come from me, but I was signed in as Sarah to give her a photo credit. Anyway, that bourbon banana bread is good stuff.

Amanda brought some of this into the office today. I think it's exactly what you're looking for -- not cakey, but moist and dense and loaded with banana: http://www.food52.com/recipes/1259_brown_butter_bourbon_banana_bread

That depends largely on what the recipe already looks like. I could hazard a few possible changes, though:
- add an extra mashed banana
- increase the oil slightly or use butter instead of oil
- add an extra egg (this will make it richer and sometimes denser, though I wouldn't exceed 3 eggs in your recipe, assuming 1 loaf, or you'll start to border on pound cake)
- if your bread uses butter, cream the butter and sugar together first, then beat in each egg one at a time (this technique makes it more cake-like)