The Aeropress has quite a few parts which can wear out or be easily lost. Finding yourself without a necessary part or just needing extra filters because you are running low is pretty common. Replacement parts and filters are very inexpensive.
Paper Filters
Rid yourself of the need of ever buying paper filters again with a stainless steel reusable filter. Use, rinse, repeat.
Rubber Plunger Tip
Plastic Filter Holder Ring
Stir Paddle