While you're at Walgreen picking up your 20 free photos, swing by the office supply isle and grab some free FriXion pens. They're erasable ink pens and, while I didn't find them to be all that great, you'll be paid to buy them!
Buy 3 packages of Pilot FriXion pens at $1.19 each.
Use $1/1 coupon found in Walgreen's April Coupon Book (found near the entrance).
Pay around $.60 out of pocket.
Send in the rebate found on the pen packages. It says you'll get a $4.50 rebate.
You'll be getting six pens in all and almost $4! Plus, think of the fun you can have with the erasable ink. Think I'll be able to get away with giving out IOUs as presents and then covertly erasing them?