Make sure they are available all around the class.
As Lisa Murphy of http://www.ooeygooey.com says, "Control the environment."
Everything in the class should be touchable. They will make patterns out of all of it.
I love natural material. Rocks, sticks, dirt. But I do not exclude man-made materials. I will use almost anything kids will touch, especially if it engages them in math. I will not, however, throw real spiders on the table. Guess what? They love the plastic stuff also. Grab those plastic spider rings off the discount table, cut off the ring part, and there you go...spider counters.
Much of my childhood soundtrack involves the whir of my brother's rock polisher in the background. He would patiently wait for months to get a hold of those smooth, cool rocks. I have noticed whenever I plop these down on a table, kids love to grab and manipulate them. Throw in a variety of colors and patterns erupt. Good thing I don't have to wait months for them now.
Seasonal goodies are good attention grabbers. As the child progresses, add a third object, so as to allow for more complex patterns to develop.