In my area, you can find loads of canning jars on craigslist and at estate sales on www.estatesales.net
(they're usually stored in the basement). You'll want to buy the rings/lids new. If you start collecting throughout the year, you'll be in good stead come craft night.
There are some great instructions online for using old Christmas cards (or greeting cards in general) for making ornaments. For the older kids, try origami ornaments. My kids had great fun making those. Even learning how to make traditional cut-out snowflakes was a treat. The paper is inexpensive (you can use scrap-booking paper for both and get 4 out of one sheet) and learning how to make the intricate looking snowflakes gave them bragging rites for years to come.
If you haven't tried www.pinterest.com
for ideas, you must. It's my new crack as a PTO member and mom. LOADS of ideas for everything under the sun and a great place to keep them all. I keep a board for each school event and pin ideas throughout the year so I don't have to go hunting for them come Easter or Halloween. It worked out great for our Fall Bash!
As for finding pine cones, it sounds creepy, but around here, one of the best places are the cemeteries. They have this fascination with planting tons of pine trees there.