Ground Bait Bowl.

The larger of the two bowls in the picture will be the version that you want to look for. Bowls of this size are made to fit the Maggot Riddle perfectly.

Most companies make bowls like this and most come with a hoop that fits to the leg of a seat box.
The most useful bowls will be made from hard plastic and round in shape. A round bowl makes it easier to get your ground bait mixed evenly, without corners to bother out.

There are waterproof fabric versions, or a plastic material called EVA. The softer bowls may be easier to pack away, but these hard plastic bowls last much longer and will not split over time.