Once when my aunt was queasy in the car and they couldn't pull over, my grandmother passed her hat back for the child to throw up in.
While I've never tried that trick, in a pinch I've caught vomit in my hands, my skirt, a blanket, a box, and a shopping bag.
Unless your tot gets carsick, you probably won't have too many of these situations.
To see what happened to me recently,
But after the episode we had yesterday morning, when I sprung from the car and made an emergency dash into Starbucks to ask for a handle bag and some napkins (thanks to the barista who gave me an entire roll of paper towels) for my daughter who had just fallen ill, I am keeping one of these in our vehicle.
The nylon TrashStash Car Litter Bag ($13) attaches to the back of the seat or stands alone. Normally used for trash, the waterproof three gallon bag could also come to the rescue when a wee one isn't feeling well.