A great product that has been successful and has continued to expand is the car coaster. Most everyone has a car. Essentially every car on the planet has a place where you put your drink. There are smaller sublimatable coasters with a notch so you can easily get them out with your finger.
These allow you to capture the attention, at least for the most part, with a beautiful art pattern or it could be a photograph of your dog or cat. It could also be a traditional monogram, a chevron pattern, or something like that.
Car coasters are easy to sell. When doing a project, there are a couple of factors involved with that product. Number one is how inexpensive is it; number two is how easy is it to decorate; and number three is how easy it is to sell. Car coasters are easy to do and could have a healthy markup on your cost.
Acrylic car coaster (Image courtesy Condé)