Soldering Iron, you can’t go wrong with a TS100 you’ll need a Lipo battery with an XT60 to power it or if you’ve got an old laptop charger that fits it that will work too 
It’s small and because its powered by an XT60 Lipo you can use it in the field for field repairs 
Also check out this thread Cheap Lock Down Quad lost of posts about the upgrades that myself @Steviegeek and @notveryprettyboy have done to our Tinyhawks for after you have gotten used to flying it and feel like upgrading it yourself.