Laminate a set of flash cards, put a binder ring around them, and toss them in your purse with a dry erase marker to entertain little ones. I don't know about the dry erase part but LOVE the binder ring!
Here's a really cute idea. Frame quote bubbles, use a dry erase marker to write funny things your kids say. When you are ready to switch the quotes, have the child take a picture with their quote and make a photo book of quotes. Our own quote board?