Water works just fine for banana ice cream.
The less liquid you use obviously, the smoother it will be. Peanut butter is a nice addition.
We've made sweet potato brownies with purple sweet potatoes, they are very dense!
Some of our old standbys are baked apples stuffed with raisins and coconut flakes, and chocolate date balls the kids call brownie bites. They are similar to larabars, you can omit the chocolate powder and use other ingredients with the date paste base.