I'd definitely wait until you're out of training and starting IOE before you invest money in anything.

I'm a cheap-butt. So here's my plan for saving money.

But you are going to need very soon:
1. Good rollaboard luggage. Get the metal frame Luggage Works or PurdyNeat. It is by far superior to any of that plastic crap. My Luggage Works bag rolls like a dream and has a heavy metal bottom plate to counter balance it. I can roll it fully loaded with 1 finger. It will withstand the abuse you're going to give it.
2. Flight kit. A cheap-o Solo bag from Staples ($75) will probably get you through a year or until you're ready to drop the $300 for the Scott bag.
3. Use whatever headsets you can for awhile, then decide based on what others are using at your airline and what you like.
4. Binders...I believe someone stated you'd be provided with those. We got cheap plastic ones at Eagle, which work just fine. No need to drop big bucks on Jepp products if you can avoid it.

The LUGGAGE is the absolute most important thing you're going to need. Everything else is trivial. If a wheel pops off your bag on the 2nd leg of a 4 day trip you're going to be lugging that thing everywhere. If you get one with crappy wheel bearings it'll be like dragging a cement block behind you everywhere. There is no room for failure of your luggage. So drop the $300 on that and you will have spent wisely on a very important investment.