Matthew, this a fine gesture on your part. My congratulations to your cousin.
I don't mean to throw cold water on your plans, but I seriously doubt your cousin will be permitted to have many personal items (i.e., toys) in his room/on his person during his "plebe" year -- especially some spiffy flashlight that might be, um, "liberated" in the name of cadet corps uniformity.
He faces an intentionally-grueling cultural shock and a rigorously-disciplined life at West Point... at least until he's an upper-classman. It's all designed to separate the wheat from the chaff... and from Mommy's apron strings... and from one's old "cheap-civilian" ways and mindset. However, if he's deeply committed, it'll all be worth it in the long run.
The penalties for trying to sneak-in "contraband" will be many push-ups, extra marching duty, loss of already-restricted liberties, and countless humiliations. And then there's the unforgiving Honor Code enforced by all.
I base my advice on my own Officers Candidate School experience -- plus war stories from old pals who made it through the various military academies.
However, if you're thinking he'll keep this new flashlight at home -- perhaps to take it to West Point a few years down the road -- then that may work. OTOH, by that time, whatever you buy him now may be obsolescent.
Perhaps some recent academy-grad CPFers might further counsel us here.