Hello! Beginner rocket builder here... What can you suggest?
* Angle Ruler/Measure
* Sandpaper (220/400/600)
* Hobby knife, #11 blade
* Epoxy (Loctite, 5-minute set)
* CYANOACRYLATE glue, thick (for fillets)
* Elmer's Wood Glue
Some of this is repetition of what others have stated, but I can't help myself.
Sandpaper: add 320 grit to your list. You can add lots more, as David said, but 220, 320, and 400 are the workhorses, at least for me, with only occasional use of 80 and 600, and far rarer use of anything higher. If I used more plywood fins I'm sure I'd use more 80 and 120.
5 minute epoxy is fine of you like to work fast, but I far prefer longer.
Thick CA has it's uses, but absolutely not for fillets. Among other reasons, when you try to smooth the fillet you'll glue your finger to the rocket. Also, I think you'd have a really hard time building it up thick enough. And this from a guy who often likes small fillets made with regular wood glue. (Incidentally, I and many like TiteBond, but Elmers is fine I'm sure.) Where I've most made use of it is in attaching fins when I have to align them by hand. With two or three drops on the root, I can align and hold the fin steady long enough for a quick (but weak) hold. The the wood glue fillets give the joint its real strength.
And speaking of attaching fins, the above method is not what I prefer. Get some sort of fin alignment jig.
I love this one, but for any motor mount larger than 24 mm you'd have to make your own adapters.
Extra blades for the hobby knife, and a few shapes may be handy. Some jobs you can use slightly worn blades for, others want brand new, or darn close to it. (I've been known to resharpen mine, but that's because I already have the sharpening equipment and plenty of practice with it.)
Razor saw.
Boxes for accumulated parts, including balsa "scrap" big enough to still be useful.
A waste basket for your build area, as keeping the bench reasonably clean is a really good idea. You can inaugurate it with your hot glue gun.
A cutting mat.
Acetone for cleaning. But beware, it will attack more things than alcohol, such as the white markings on the cutting mat. (Learned that one the hard way, I did.)
These are a few of my favorite things. That is, the tools I use most, or miss the most when I don't have. I don't disagree with dhbarr about accumulating things gradually, as needed.
Thin CA is very useful but be careful with it.
Oh my Figure of Speech, yes! The stuff seems to be less viscous (i.e flows easier and quicker) than water. Darn useful, and a little scary. Sometimes I've used it on my fin roots, after the two or three drops of thick and before the fillets, and more than once I've stuck my fingers to body tubes. And (as others have said) it's good for stiffening and strengthening balsa, paper, cardboard, and the like.
Advice done, conversation commencing. About the Arduino altimeter, is that because you
want to build your own altimeter? There are many good and reasonably priced altimeters on the market; if you want to build you own then by all means go for it. If not, just buy one.