Kids always want the toys and books they don't have, so arrange a swap with families from school. My students love Fridays because they each bring a favorite toy to share (labeled appropriately) and they get a new one each week to play with. Books, CD's and movies work the same way.
For fun craft projects try
ENCHANTED LEARNING HOME PAGE, they have free activities and coloring pages on just about everything. Really good for rainy days and most of the materials are around the house items.
For school lunches try to purchase bulk family size chips or cookies and wrap in foil or reused bags (instead of individually packaged items) Buy a cheap one time plastic drink bottle to send with water or milk each day for a drink. (works for moms too!)
On car trips, pack a lunch and stop at a rest stop, not fast food joints. You avoid the temptation of eating out expensive and the kids can run around.
Check at a local butcher for extra paper and let the kids color it for you to use as wrapping paper. For kids gifts, just write the card information right on the package with a marker. Save $ on a card since most kids probably don't care anyway.
Deliberately make large portions of meals and freeze extras. Food is cheaper bought in bulk and when you pull them out of the freezer it is almost like eating out since you don't have to cook!