3 Axis Microlight.

Chinagraph on a long stretchy elastic hanging from cockpit roof.
Current Chart.
Skydemon on a 7 inch tablet on the panel.
Handheld radio clipped to panel.
Headset
Inexpensive wristwatch.

I like being "over equipped" compared to my flexwing days :)

Don’t buy anything before you start flying.
Be patient and frugal and you’ll find people giving stuff away or on the cheap.
Long forgotten boxes in the back of the hangar, nobody remembers who owns them. Treasure hunt.

I use an A4 kneeboard, with A5 clear plastic sleeves on a binder, filled with pretyped paper, with boxes for any information I receive during the flight and appropriate spaces left. I then use fine non permanent markers to write down anything pertinent on the plastic. Really cuts down the memory workload from behind the controls and it doesn't waste paper. Aerodrome charts go underneath in A4 for easy viewing. And then it has a clip on the right for PLogs etc. I've found this invaluable in making flights easily manageable.

Lightspeed Zulu 3 (absolutely invaluable, the clarity of ATC communication compared to school headset is incredible, as is comfort). Checklist, watch, map, diversion plotter.

And the obligatory pair of Aviators, of course ;-)

ppl general:
- A5 kneeboard
- large nurse's watch (I don't like stuff on wrists and hands)
- cap (I don't like sunglasses much)
- head set (probably supplied)

specific for ppl exam flight:
....pilotshop.nl/contents/en-us/p408_Wind_Protractor.html
Never used it since but excellent (easy and quick) for the one occasion when one is required to supply heading and time to a mid flight alternate.

Making and learning an exhaustive pre-flight checklist (including documents etc. and bathroom visit) was useful too as I remember.

Starting out
 

Sean,
Apart from the knee board you've already got, one of my first purchases was a headset. The school provided one, but it was something I wanted (rather than needed) and bought a mid-spec pair of David Clark's. Glad I did, and still use them to this day.

The only other things that I got early on and still use are:
- my flight bag; I got one of the first Brightline bags when they were launched (back when there was only one version). There are a stack of different ones to choose from now. It kept all my maps, books, notes and flying stuff together and easily accessible.
- flying jacket; (not a big showy sheepskin thing before you start!), one of the cheap Transair things. I like fresh air in the cockpit, but don't like being cold - a regular occurrence learning in a drafty 152. The cut of the jacket means it sits comfortably on my waist, there's plenty of arm movement and there's no collar to interfere with my headset when I look around. I also make use of the pen holder on the arm because I found putting pens back on my knee-board a bit of a fiddle.

[And no, before anyone starts, I don't wear it anywhere else apart from flying because that's not my thing. Yes, I really do take another coat with me so even if I'm just stopping for groceries on my way to/from the airfield I'm not strutting around in a flying jacket. It's bought for a purpose and serves that purpose]

TPP

Here's a tip; Don't bother with a stopwatch, get a wrist watch with a visible sweep second hand (not a Brietling it's far too cluttered and you don't need stop/start buttons)) and time parts of a minute by just looking at the second hand and noting where it is etc. This is far easier and takes less effort than clicking a stop watch all the time.
FF

In a super cub, paper map on the back seat (under the cushion or handed to the passenger if I have one so it can't blow away). A6 kneepad, small tablet running sky demon duck taped to the kneepad. Plot in my shirt pocket, pen on the kneepad. Watch velcroed to the panel so I can change it when the battery dies. Spare glasses in the map pocket with anything else potentially useful such as airfield visual charts and a bottle of water. Don't often need the paper map.
In a balloon (hopper, no basket) the tablet goes in a map case round my neck, altimeter on my wrist, radio if I take it in my pocket, with safety string. Ditto phone for retrieve. Glasses in a pocket on the harness, in a very solid hard case. So far I've not trashed the tablet on landing, but I have managed to lose a phone, at least until crew called me on it. Paper map stuffed inside my shirt or in an under seat pocket not accessible in flight. I can always get it out after landing.