If you can make them, frost arrows are the weapon of choice against Sea Serpents. Not only do they have weakness to frost, it slows them down. So if you want to kill that serpent, it is not that hard, or shoot a frost arrow at it, and when it hits, sail away as fast as you can with the wind at your back. I know what you mean, "serpent waits there just next to my corpse ..." I have had that happen. Lucky for me I was playing with my son, and he sailed right up to my corpse, and I recovered all my stuff while leaning over the side of the bulkhead. I have seen a few serpents, and marked them on my map, and they were still in the exact same location many days (irl) later.

I always keep a chest at the foot of my main spawn bed, with a second set of armour and weapons, with 1 of each food item I am currently using. Keep in mind also, there are no penalties for dying a 2nd time, if you are under "corpse run" conditions, so it pays to try and reclaim ones items as fast as possible, even if it takes multiple attempts.