Beginner's field box (before solo):

Fuel
fuel pump (or bulb)
3 spare props
a few spare screws
1 or 2 spare glowplugs
Medium CA
5 min epoxy.
Clear packing tape.
Rubber bands if required for the model.

THAT'S ALL!!!! Yes, I WANT you to depend on the instructor for the glow ignitor and starter, and any other support equipment. If the instructor isn't there you shouldn't fly.

If you need repairs requiring more than some CA and epoxy (clear tape to patch punctures in covering) you need to take it HOME to fix it.

After solo ADD:

Glow ignitor
Expanded scale voltmeter (ESV)
Electric starter and battery
assorted screwdrivers, allen keys and wrenches appropriate to your model.
spare clevices

Some more repair stuff might also be added.
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You can get by on that much for the rest of the time you are in the hobby if you don't get into competition. (Instructors should bring more... and they almost certainly will.)