Nomex & Cotton
I've been on fire once before in my life (not in an airplane) and it is not something I'd wish on my worst enemy. So for my first flight, I went with the following:
Nomex Flight suit. Search eBay for a new old stock one and save some money.
Long sleeve cotton shirt underneath. You can buy fire resistant (FR) shirts from quite a few places too. I ended up getting an Oakley FR Carbon-X shirt for some of my flights, but only because I was flying faster than I could do laundry for my long sleeve cotton shirts, and I was flight testing in the middle of summer and would soak my shirts in sweat.
Lightweight, but calf-height wool socks.
Nomex high-top shoes. You can get them from the race shops online (Pegasus Auto Racing is one of my favorites). I have Piloti brand, but Simpson sells similar ones.
Leather gloves. Thin TIG welding gloves are great low-cost alternatives.
I wore a helmet (MSA Gallet), but no parachute. That's an entirely different discussion on those choices.
That's it. After my flight testing was done my flight suit and shoes have pretty much been sitting in a bag at the hangar. Everything else you can use in normal circumstances.