Who doesn't like index cards? With my retail store they come in especially handy. For instance if you punch a hole on one end you can use them for restock hangers behind existing stock; or use the blank side for small sale signs etc.
These are the best for taking quick notes jotting down a recipe on etc. Keep grandkids stocked with them for school notes upcoming projects etc. ALWAYS have in the kitchen beside my sofa and in my purse.
What can't you use index for? I use this mostly at work. I am a teacher and I use this as a teaching tool. I use it for display and student use. The are good also for flash cards too. They are normally reasonably priced but you can get them cheaper during the Staples sales. I buy several of them when they go on sale.