The biggest problem with Cub Scout shows is the range of ages. The difference in ages is pretty big. The 6/7 year olds (first graders) like certain things and the 11/12 year olds (fifth graders) like other things. As you said, the parents will be there too.
I would guess you would be performing for around 100 people (5 dens with 10 kids each and at least one parent?), so the effects need to be able to be seen by everyone.
That being said, I've done Cub Scout shows before and they are a lot of fun.
Some of the effects that I think would be great are:
~Linking Rings (can be seen by everyone and can use a volunteer)
~Invisible Deck / Brainwave Deck (if you use regular cards, spectators can verify that the card is indeed what was named)
~Vanishing Bandanna (which I think is what you are calling disappearing banana)
~Comedy Cut and Restored Rope (Professor's Nightmare)
~Snowstorm in China (make snowstorm with napkin, glass of water and oriental fan)
~Ring flight / Spellbinding Boxes (ring or coin disappearing and going to wallet, key ring or nested brass boxes)
~Tagged (by Rich Ferguson)
~Bill in Lemon
~Magic Candy Maker (makes candy out of a cup of sugar - more for the younger kids, but everyone likes candy)
~Change Bag / Silks Routine (very visual)
~Jumbo Card Effects
~Airborne Soda (pour soda and let go of glass which remains suspended)
~Healed and Sealed Soda
I don't think the D'Lites or sponge balls would work well in that type of setting.