I am a Home Economics Teacher, a far cry from an art teacher,
however I think I have a couple of suggestions for you. The
first is to take some magazines with you and have them cut
out pictures or words and make a collage on poster board.
You could have different themes: self-esteem, feelings,
wishing well, etc. The other suggestion is to cut different
colors of construction paper into really small squares & have
students make a mosaic (I think that is what it is called)
using those squares of colored paper of something that they
are familiar with or an assigned picture.