"Must need" can be easily defined as 'anything replaceable or reasonably repairable that would put you out of flying the the day'.

Props
Glow plugs
Fuel line
Prop nut and/or spinner
Wheel collars and a wheel
Servo screws
Other hardware
Wing and landing gear bolts (if used)
Rubber bands (if used)
CA and kicker
Other hardware that might fall off
100 MPH tape (clear packing tape)

It's not really a large list. All of my spares AND tools are in a two tray 13" toolbox I got from Big Lots for about $5.

As for parts and tools: take only what you need but take all you need.

Dr.1