I'm glad to hear you want to get into waterfowling, man! Be warned... it is addictive, and it will cost you more money. lmao
Ok so here are some of the basics that I think would get you started into duck hunting:
1-2 dozen cheap mallard decoys... Greenhead Gear, Flambeau, or similar.
A polycarbonate double-reed duck call... Echo, Zink, RNT, Buck Gardner all can be found for 30 bucks or less.
Kent Fasteel #3s or #4s... this steel shot is inexpensive and very well-made.
Waders... *see below.
Outergarments... **see below.
*Waders - These are a necessity for duck hunting in marshes and swamps, however the brand/type/thickness are a matter of personal preference. If you're unsure of your commitment to waterfowling and want to keep things cheap, you can pick up some uninsulated rubber or canvas waders that won't break the bank... However, these are cold, these are uncomfortable, and these are not very ergonomic IMO. If you think you'll be into waterfowling for a while, do yourself a favor and buy some quality neoprene waders. For a good pair, you can expect to pay anywhere from $150 to $250. I have a pair of Cabelas 5mm Supermag waders that have been absolutely great. I think I paid around $150 when they were on sale... normal price is around 200 bones. Neoprene is warmer, more comfortable, and more ergonomic.
**Outerwear - Again, you can go cheap if you want, or you can go for broke... it's all about preference. Here's something to keep in mind... When it comes to waterfowling, generally the shittier the weather the better the hunting is. In order for you to sit through the shitty weather comfortably, you're going to need some quality, warm, and preferably water-resistant outer garments. There are a ton of camo patterns that will work just fine for waterfowling. If you're hunting in flooded timber areas, the same camo patterns you use for deer hunting will work just fine. If you hunt mostly swamps and marshes, a lighter cattail-like pattern may be best. I'm a fan of Realtree Max-4 for waterfowling camo.
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Goose hunting is an entirely different animal. The calling is different, the setups are different, and generally more gear is needed. If you're hunting fields for geese, you'll need a layout blind and more decoys. If I were you, I'd pick up 3 or 4 goose floater decoys and use them in conjunction with your duck hunts... basically hoping for a "bonus" goose every now and then. Try to hook up with a TOO brother that's fully set up to goose hunt and go on a few tag-along hunts to see what it's all about. There is a butt load of effort and expense that goes into shooting just couple geese, so take goose hunting for a test drive before completely diving into it.
Good luck!!!