Well, your gun probably tops the list of necessities, but second would have to be a knife.
If you're going to make tiny cuts and salvage the relatively small amount of meat from a duck, you're only going to be able to pull it off with a good, sharp knife.
The thing with a knife, though, is that it's useless if you don't take care of it. A knife can go dull quickly if you use it a lot, and then it's just dead weight. Sharpening your knife is a crucial, yet often overlooked necessity to success in the waterfowl woods.
Aside from any handy work you may be faced with when you're in the field, you're hopefully going to be doing some cleaning as well. If you're blade is dull, you're in for a long day of misery.
Any old knife sharpener won't do it either; you need something tough that will go the distance without you having to replace it. You can't go wrong with the Work Sharp Combo Knife Sharpener. It's not too expensive and it can sharpen any knife you own.
Not only can this sharpener manage all sorts of straight-edge blades, it can also handle serrated knives. Using a complete bench-top product like this makes all of your tool maintenance quick and easy.
Make sure you're prepared with Work Sharp when out waterfowl hunting this season.