He has a knife. He doesn't want to give up his spear, but he likes having the idea of a flashlight so much--something to combat the darkness and, maybe, the nightmares--that he has to acquiesce somehow. He has to compromise.

It's not like he isn't completely unarmed, right? He can still get out if things get rough.
"Fine. But if you try anything, I can still kick your ass."

And, slowly, the spear is lowered.

"Now gimmie."