1. The ‘lock pick’ tool . This can be made from the wire from a standard hair clip using 2 pairs of needle nose pliers. The tool should feature a small small hook at the end (radius 3-4mm), and also a handle (a coil of wire covered with electrical tape)
2. The ‘blade’ tool. Take a hacksaw blade, the thinner the better. Cut a 100mm length, then using a file or a Dremel with circular filing tool, remove the serrated edge of the blade and create a rounded edge at one edge. Then cover the other side with tape for a comfortable handle). Finally, try to create a slight taper on the rounded , so that the two faces of the tool make a sharp edge.
3. Files. You may need half a dozen sets of carbon steel needle files for a single instrument. You can buy them quite cheaply from most hardware stores. These wear out quicker than larger files but unlike large files, may be more effectively used for ‘scratching’ the reed due to many of them having a usable point or a sharp edge. Scratching, though it may appear the deface the reeds, is arguably better than filing (where possible) as it is far less likely to create any ‘fracture’ points, or ‘grooves’ across the reed tongue (which may increase the chance of a reed cracking under stress)
Warning. If your files become blunt, stop using them, (especially on the higher reeds). You will have to press harder, and far more manipulations will be required in order to affect the same change.
4. A bag of assorted valves. You might have to ask your local accordion dealer for these (I did). They are incredibly difficult to source.
Leather or plastic valves are both fine. Acoustically it makes no difference at all as to which type you choose. And there really is no perceptible difference in speed of response between either. The only consideration might be longevity.
Larger valves are generally more useful as they may easily be cut to size, but an array of smaller valves is quite useful.
5. An Electronic Tuner. I can highly recommend the app ‘Cleartune’ for the iPhone or iPad. It does everything you will possibly need, very quickly and very well.