Short eating knives should be up to 6" long, though they may be shorter. Eating knives are usually suspended vertically from the belt by a single loop of leather stitched or riveted to the sheath.
Eating knives are usually sharp and are an essential part of re-enactment (assuming you want any food!). For safety, sharp knives may not be taken onto the battlefield, though the empty sheath may still be worn.
There is also an example of a small folding knife from Canterbury, possibly used in manuscript production.