I use index cards every day to keep my to do lists. I carry them with me to meetings and write what I need to do on one what I need to purchase on another and what I need to follow up with others on yet another. That way as I check off my lists I can just file them with a date or toss the ones that I don't need.
A lot of people these days don't use cards to organize their information. I do. As an historian I am compiling a chronological file of information on 3 x 5 cards. The cards are in general hard to find and expensive. Staples gives the best value. Thank you.