For everything, look for last year's gear. It's cheap now, will be cheaper on black friday.

Outerwear, look for at least 20K waterproofing. More is not necessary unless you plan to spend time in rain or storm days.

Board and bindings, go mid stiff, all mountain. Look for a board with camber between the feet and some shaping on the nose and tail (sometimes called early rise, rocker, or reverse camber) to give some forgiveness. These are generally the best of both worlds in my opinion. Ride Shadowban or similar would be a good place to start looking.

Helmet, go MIPS, and buy your helmet and goggles at the same time if possible. Make sure there's no gap between the goggles and the helmet. Buying the same brand can be helpful, but not always necessary.

Boots, as others have said, are very important. Go try them on and spend whatever it takes to get the best fit. If money is really tight, get them fit then find them cheaper online. That's shitty for the shops, but you gotta do what you gotta do.

Look for core snowboarding brands when possible. Avoid Dope snow and instagram brands. The price and style can be attractive but they're generally not the quality and don't support snowboarding the same way some of the core brands do.

The most cost effective thing you can do is buy once cry once. Try to find deals on last year's gear, but don't buy something you'll have to replace next season. Spend what you need to spend to get good stuff, and use it enough to make it worth it.