This portable potty seat has rubber legs that flip up for stand alone use. Simply line the seat with a disposable bag and once your child is finished, tie the bag and toss it in the garbage. Flip the legs out and use over any toilet seat. It folds flat for easy storage, so keep it in your car to have it handy wherever you go.
See also the compact Disposable Bag Holder which includes a roll of 20 disposable bags.