One neat idea our school does (grades 3-5) is have matching colored shirts for each class. This year they actually had them made, but the last few years they made them. Each child brought in a plain white t-shirt. If some aren't able to, many parents are willing to buy a pack of 3 white t-shirts, they are inexpensive enough. Then each class (or you could do by grade if you are doing a very large group such as grades k-8) picked a color. Each child scrunched up their t-shirt and put rubber bands all over it. One mom from each class took them home and put them through their washing machine with some dye, sold in the grocery store. Very easily done, takes one load to wash and dry,when you take the rubber bands off they are all tie dyed a bit different and the children were so proud of them, and really gave them some team spirit!