And of paper systems, along with my Moleskine notebook, index cards are my favorite. They’re cheap, they come in stacks, and they’re infinitely adaptable.

How can using index cards keep me organized, you ask, ever so quizzically (almost mockingly)? I’ve already got the ultimate web apps to do that?

Glad you asked. Here are just 20 things you can do with the ever-handy index card.

1. Make a to-do list. Probably the most obvious, but what’s great about using index cards for this is that it forces you to be concise. I write my top 3 Most Important Things to accomplish today on my Today list.

2. Take notes. I’m in a meeting with someone, and need a handy medium to take notes … so I whip out a blank card and keep bullet-point notes. Later, I’ll transcribe any necessary actions to my action lists and file the card.

3. Create a PDA. By now the Hipster PDA is pretty famous among productivity circles. It’s a way to keep all the info you need with you anywhere you go, using only index cards and either a binder clip or a rubber band to hold it together. Very handy.

4. Make context lists. In the world of Getting Things Done, context lists are central to organizing tasks. You can create a card for each context — computer, home, errands, etc. And the cool thing: unlike other organizing systems for context lists, with index cards you can place the context card where you need it. In other words, the @Home card is at your home, the @Computer card is next to your computer, the @Errands card can be taken with you.

5. Keep track of projects. There are a million ways of keeping track of all your projects. But few as simple as writing a list of them on an index card. And if you need to expand, you can create a card for each project that needs an outline.

6. Create a crazily obsessed organization system. Personally, I love this one: POIC (Pile of Index Cards). Created by a Japanese guy obsessed with organization, he took GTD to the next level. It’s a bit much for me, but the fetish-ness that he brings to the index card is just wonderful.

7. Create a novel. One card at a time. Nabokov, most famously, wrote entire novels on index cards, composing the novels in bits and ordering them into a book. But other writers have used similar methods using index cards.

8. Leave a note for someone. I like to write notes on a card when I’m forwarding a document or delegating an assignment, clarifying the actions that need to be done to the recipient.

9. Create a quick reminder. Need to remember to do something in the morning? Write it down on a card and place it somewhere you’ll never forget. I like to write down a reminder while I’m on the go, one per card, and then toss it in my Moleskine. When I get to the office or home, I just transcribe the reminders to the appropriate list (or do them immediately).

10. Make your life’s short list. Want to figure out how to simplify your life? Make a card with the 4-5 most important things in your life — your short list. Then focus your life on those things, eliminating all else. By putting this short list on a small card, you can post it somewhere visible and keep those priorities in mind, always.

11. Trick out your Hipster PDA. The regular version not enough? Add a Levinger Pocket Briefcase and some cool printed templates.

12. Organize your research. Regular notes not good enough? Use this system to keep things organized, geeky and useful.

13. Flick them at people in meetings. Ninja-star style. This might not go over too well in some corporate cultures. Be prepared for retaliation.

14. Develop consensus. The Card Carousel technique is actually an interesting way for a group to share ideas and come to a decision.

15. Organize your bills. Create a card for each bill, writing the name of the bill at the top. When you pay the bill, create an entry on the card. This way, you have a running log of all the bills you pay.

16. Doodle. Bored at a meeting? Use a blank card to doodle. Or if you’re more artistic than I am (and it would be hard not to be), you can use it as a mini-sketch pad. Just don’t let your boss see the sketch you did of him in his underpants.

17. Keep recipes. An old-fashioned use for index cards, to be sure, but one that works well. A card is perfect for a recipe, and if you keep them in a handy box, you’ve got them all organized alphabetically, for quick access when your kids are crying from hunger and you can’t remember the Stroganoff recipe.

18. Make a paper airplane. Not as light and far-flying as a model made from lighter paper, but cute nonetheless. Again, another great diversion for those weekly staff meetings. Bonus points: write love notes on them.

19. Flash cards. My kids use these to study for tests. They work well.

20. Origami. OK, I admit that I don’t know how to do this. But how cool would that be?

21. Shopping lists. Keep one posted on the fridge, jot down things as you run out of them, and take it with you on your shopping trip.

22. Book lists. I like to keep two book lists: one is a running list of books I’ve read, and another a list of books I want to read. When I hear of a good book, I add it to the list.

23. Handy log. Want to keep track of your spending, or eating, or anything else? Keep it on an index card, which you can carry wherever you go.

24. Organize your entire home. GTD not overboard-organized enough for you? Try the SHE system (Sidetracked Home Executives). They use index cards to organize everything: tasks that need to be completed on a daily, weekly, monthly, and seasonal basis, cleaning, decluttering, correspondences and more.

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