Find the iron in cereal
It's an oldie but a goodie for minerals.
There are several ways to do this, so try them at home with to see which works best for your supplies.
Buy three boxes of cold cereal. Get one with lots of iron (check the side panel), one with some, and one with very little. I don't remember all what I used but I think I used wheat chex for my lots-of-iron cereal.
Crush one cereal in a zipper bag. Then, shake a clean (wash it?) magnet in the bag with the cereal crumbs. Pull it out and wipe it on a clean paper towel. The black stuff you wipe off is iron. Repeat with other cereals. Which had more iron?
Or, mix the cereal and a bit of water in a blender and again, dip a clean magnet in the "soup" and look for iron on the magnet.
Another variation is to crush the cereal into a fine powder and put on a paper and run a magnet under it and the iron added to the cereal should move with the magnet.
Have the kids look on the sides of cereal boxes for things that are also on the periodic table. In addition to iron, they'll find magnesium, copper, zinc, manganese, etc.
Another fun activity is to draw a rough body outline on a piece of paper and make copies (one per kid). Draw a line horizontal line across about where the chest is to represent the percentage of water that we are. I can't remember the exact percent but it's something like 70% (look it up?). Anyway, have the kids come in and weigh themselves on a scale and then multiply their weight by .7 and they come up with how many pounds of water that they are and the difference (.3) is how much other stuff they are. So, if my ratio is right (and I doubt it is), a 50 pound kid is 35 pounds of water and 15 pounds of other stuff.
Another thing you could do is go to the grocery store on a field trip for a scavenger hunt for nutrients (perhaps after teaching the unit). Have each little group of three to four find excellent sources of protein, vitamin A, vitamin C, iron, fat, etc. They can use a digital camera to take pictures of their trip or they can use a clipboard and pencils to write down what they saw.