Copy paragraphs from textbooks. Time-consuming but forces one to slow down and think.
Memorization mnemonics. Shuffling through index cards to associate numbers to words. See Mind Performance Hacks (2006) from O'Reilly.
Make notebooks with cheap filler paper, high-capacity stapler, and duct tape. Use G2 pens or archival quality ink.
Make your own index cards: fold in half and then into thirds; cut those into rectangles. (Still on the lookout for good storage.)
Shade paper with crayon. Carpet is smoother than desks. Envelopes are a good way to iterate color combinations. Pick colors at random.
Convert mailed coupons into CSS. You get salable graphic designs and color palette for free.
Break down milk cartons for free cardstock.
Prime cardboard with paint for a cheap canvas.