You are going to need a few of these for the various baits that you will inevitably end up taking with you. The most important of these will be maggots.
Good bait boxes will have a tight-fitting lid with plenty of air holes to allow your bait to breathe. Some boxes will have lids without holes made for containing hard pellets. Obviously, these do not need to breathe, but they do need to stay dry.
Bait boxes are usually available in 1 pint, 2 pint, and 3 pint sizes. All will have their uses at some point. The 1 pint for a small amount of bait. 2 pint for general use, and the 3 pint for larger amounts of bait as well as straining pellets.
You can never have too many bait boxes.
Keep your bait boxes clean. No one likes smelly bait boxes, particularly shop owners.
Clean boxes will not taint your bait either and make for better bait.