To help students develop a more accurate conception of what it's like inside a (eukaryotic) cell I started asking them to imagine a plate of spaghetti and meatballs stuffed into a small plastic bag. There would be no empty space and nothing would be 'floating around' in there.
After using this analogy for a while I decided...why not do it as a demo. Here's a video from lecture:
I always use a clean bag and gloves so I can eat the spaghetti for lunch later. The meatballs represent organelles while the noodles taking up most of the space in the bag represent cytoskeleton. I do this demo before covering motor proteins. The spaghetti bag helps students understand the role of motor proteins...when large structures move inside a cell they are being dragged through a dense matrix.