The first question is: Where do the last names derive from ?

Most of the last names (or family names) derive from either the job or the area where our ancestors lived. Normally not our ancestors, but their fellow citizens are responsible for our names. The continuous use of an additional name slowly transformed it into a last name, but like nick names the choice lies with the user and not the subject of the name.

Some examples for job names are
Miller (in German Müller) and Smith (in German Schmidt).

Examples for area names are
Ford and Field, but more often area names consist of more than one part.

The name Kreienkamp consists of the two parts 'Kreien' and 'kamp', where the last part tells us that it is an area name.

Kreien (also Kreyen, Kraien or Krayen) derives from the bird species 'crow'.

and

kamp (also kampf or kampff) has the meaning of field (battlefield, history most likely doesn't know anything about this skirmish or battle any more).

If you combine both parts, it tells you that someone who lived near an old battlefield had a good chance to be called Kreienkamp. This doesn't mean that he fought in this battle. He could be everything from a farmer to a veteran who settled at the field where he fought his most important battle. The information the name tells us, is that the ancestor of the name lived near a field visited by many crows.

Remains the question: What do crows and a (battle-)field have in common?
The simple answer is that crows eat carrion (why do you think there is a species called 'carrion crow'). In the good old days the dead and wounded of the losers (some of the victors as well) were left on the field of battle after victory was achieved. They fell victim to plunderers and carrion eaters like pigs and crows. Yep, pigs eat carrion too.