Yeah, I’m kind of seeing it as three different options. The first is that whatever they were traveling on that crashed had these things, the other’s like you said - it was sent with arrive too late, or #3 they’re dumb and didn’t notice that all the boxes floating around were exactly what they need. Very unclear
I think the joke is that the guy is unbelievably cartoonishly lucky that all those things are floating too him on a deserted island all at once, put in juxtaposition with the one element of bad luck (that he's already long dead).
The second one seems most likely as there are indications that the boxes are only just arriving. Also there is an old meme about sending away for items delivered from Acme, like the coyote in Road Runner cartoons.