I just had my third colonoscopy about 2 weeks ago. This was the first time I tried a low residue diet 5 days prior to my procedure. I didn't have to do it; just did so voluntary. It was on my list of procedures and indicated for people who trend toward constipation. It is not a "must do" but it supposedly makes it easier for the prep to work/clean you out.
I will say that for this prep, even using the same solution, I was definitely more cleaned out at the end then previous preps. That said, my previous preps were fine also.
Basically I ate the way no one is supposed to. I had pancakes for breakfast, lots of white rice, white breads, lean turkey and chicken cuts, mac and cheese, ramen, etc.
The day before the prep I made a batch of Island Pineapple Jello (not a fan of lemon), sipped on bone broth, which as protein in it and help. I am not a soda or juice drinker so I didn't rely on all that stuff, although during the actual drinking of the prep, I used ginger ale as a bit of a chaser.
I was told that you could actually eat gummy bears. Most top brands are just a thicker geletin and they turn to liquid in your body. It was nice to have something to "chew" but even then I didn't do too much of that. Lidl Brand Sour Gummies have a majority of white and yellow gummy bears in their packages.