arround christmas and easter, i keep some of the gift wrap, and chocolate foil (ya know the coulored easter eggs one?) sometimes cut it up, or rip it up and they glue it onto paper, toilet rolls ect. cotton balls are great, so is cut up sponges, diffrent things to glue down, leaves and sticks are also favourites.
if you can get sponges big enough, cut them into shapes and youve got your own paint stampers (cheeper then store bought ones to)
not one of my faves, but the kids love it, playgroup has a "messy day" the 2 fave things all the kids love, is the foam table, homebrand shaving foam and food colour they mix it, make pictures in it (id recoment a good thick plastic cover for the table/surface you use!) also there hands may stay the color you chose for a while.
another mees day fave is a large container of the gelli baff stuff.
ahh theres heaps but ive just gone blank!! will come back if i have any "brain waves" very unlikly!