Maybe he didn't expect to get smashed in the head with a boat oar and would have grabbed.
Interesting that it's infront of the other outriggers, as it seems likely Locke and company will end up in those boats too. Since Ben is still on Hydra, he has a chance to reclaim his property at the very least.
I've wondering when they'll let us know what's in it.
I noticed this as well but I didn't get the impression that he was abandoning it. He tosses it against the side of one of the out riggers and it makes a thud. felt to me that he was a.) putting it somewhere out of the way while her prepares the boat, and b.) making you the audience aware that he is in fact carrying something. I would wager in the next few episodes he will wake up and go straight to that pack and pull something out that is amazingly useful at exactly the right time.