Every usual pillow has a chance to become fighting one. Only thing we have to do is giving it a war paint.
Give your preference to the pillow with plain white surface because it is ideal for painting. However any light background is appropriate and texture on surface can play a role of drawing grid.
I like fighting with big and heavy pillow. 70x70cm (28x28 inch) is big enough. Weight depends on pillow filler. The natural filler gives much weight. Artificial fiber makes the pillow harmless.
Choose a war picture for your pillow. The picture should be simple because we make it quick and cheap. I picked sight pictures.
Choose funny picture if you look serious anyway. I picked Antarctica map and Coat of arms of Berlin basing on old infamous russian joke http://www.youtube.com/watch?v=Z_pC-xlcLv4
Get markers. The simpler picture you have chosen the fewer markers you need.
Get to a park. Let people see mysterious act of bringing casual art to life. If you notice children that look at you and want to take a part, you do things the right way.
Draw the war paint. Just draw it and have fun. Make lines with fast and long movements of your hand. This way paint does not soak surface and filling of the pillow.
As you can see the lines are not ideal, but shape can be improved a little bit on filling stage.
Fill the shape with color rectifying it as much as possible. I slightly changed the contour.
I wanted to draw inverted version of the sight on the other side of pillow.
I found bandage in my backpack and made a cross over the pillow to make white spaces between parts of the sight . You can use any kind of tape to do so.
I drew it rather quick than clean because the time of fighting approached.
I wanted to present this pillow as a gift to my friend. I left the bandage on the pillow as a ribbon and made the bow. Yet the bandage may be useful after fighting ;)
The second pillow was supposed to be painted in Antarctic map on the one side and Cote of arms of Berlin on the other.
But I had time only to draw Antarctic map. Berlin's Coat of arms was too complicated in fact.
The fight started. The most powerful pillow unsurprisingly was the first one.
I spended 30 minutes per one pillow's side. If you have more time, you can use more sophisticated technics and pictures. Fight with pillows and have fun!