Clear soup, jello. Jello, but not red jello, see through liquids, water, clear soups can make you feel full. Sometimes the bowel prep itself involves large quantities of liquids too.
No. Bowel prepping stinks. Unfortunately it is the only way for the colon to be clean so a colonoscopy is effective. The cleaner you are, the better view the doctor gets with the scope. Bowel prepping for surgery may reduce the risk of infections, but there is conflicting evidence at this time.