Many years ago (when I was poor) I designed and scratch-built a 2 meter sailplane using:

1 A Razor Blade (From a razor)
2 Some Drill Bits (Note: no drill, just twisted bits by hand)
3 Sandpaper
4 White Glue and epoxy
5 A clothes Iron (For the covering)

So those are the "Essentials", but I wouldn't recommend it (Unless you're poor )

Here's what I would recommend:

Essential:

Hobby Knife w/ #11 blade
Medium CA
Thin CA
30-Minute epoxy
Drills
Basic hand tools (Pliers, screwdrivers etc)
Allen Wrenches
Pins
Clothespins (For clamps)
Sandpaper

Extras which are very good to have:

Razor saw
Clamps
CA Accelerator (Use sparingly)
Dremel Tool

Other important things (that you will need, but for the short time you will need them, you could borrow them from another flier):

Incidence Meter
Covering Iron
Heat Gun

And finally, the three most important things:

Cigarettes
Beer
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