I'm very happy to hear your father survived the downing of his plane and was able to evade capture. I can't tell from the picture but one piece looks similar to a magazine from a Colt 1911A1 pistol, which you father may have been carrying at the time. It might even have been an extra magazine stored onboard, not the one in his pistol, if he was carrying one. I would think that if he had a 1911A1 with him at the time it would have been in a shoulder holster that many aviators used or possibly a conventional belt holster, but I would think that he would have kept that with him at all times.
Here is a picture of a G.I. issue Colt .45 M1911A1 magazine. Keep in mind that these were made by several different companies and subcontractors so the size and pattern of holes on the side varied over time and from one manufacturer to another. Many of these magazines were made by companies that made shavers and other household items.
Ask your friend to find some good pictures of one of these magazines and compare the curvature and size to a known example and you may be able to exclude this possibility. Let me know if you need better pictures or details and I can provide them. Good luck in your search.