A technigue I use is to crop a picture to the right size to fit on a banner. Then make a color photo copy or print it on a heavy grade paper. If you have acces to different colors and grades of paper the task is even easier.
If you can get a hold of it, a tan bonded paper stock might work best. The picture will appear a little darker and you will have a little texture to your banner. Cut out your banner and mount it on your banner pole.
If you wish to give it a weathered look, you may want give it a wash with several thin coats of flesh wash or thinned down brown ink. You can also distress the banner, by heating a pin head under a match and the pressing it to your banner while the needle tip is stil hot. The will make little burn holes that will look like bullets have passed through the banner.
You could also burn the edges or instead of cutting the paper originally use the fold and tear method. Fold along the edge of the banner, where you would normally cut with a scissor. use a straight edge or fingernail to crease the folded edege. tear along the folded edge. This will give the edge of the banner a slighty frayed look.
For fancy banners, you can use string or yarn to make a tassel or brocade off of the banner. To seal the banner, you can use either PVA glue or brush on varnish. if you wish to add action to your banner roll one of the corners up in a large circular object (a thick marker or wooden dowel work well).
As the glue or varnish sets, the banner will retain this curled shap making it less static. If it is a large flag like banner, you may wish to add a wave in the center, so that it appears to be flapping in the wind.