Here is a list of things I started with when I started waterfowling five years ago:
1. a good pair of waders (there is nothing worse than wet feet)
2. a good camo jacket (nothing fancy)
3. grass woven mat (bass pro shop sells them for $10 for a 4 ft by 4 ft chunk)
4. 12-24 floating decoys with wieghts (decoys are typically sold in half dozen sets and I chose of variety of species that way I can use them both early and late season)
5. Baby mojo duck (sold for around $70-$80)
The mojo duck is an absolute neccesity if you are serious about getting opportunities to shoot ducks. I've had friends who swear that they enjoy the "old-school" approach with no mojo but I can tell you my buddy and I went hunting 12 different times last season and we both limited 10 of those times with the mojo.