When one is a qin player, other than having a qin in possession, there are certain other extras one must (or ideally should) have in the qin bag pocket. These items are mostly common-sense yet many only have one or two and are thus ill prepared for all eventualities that may arise. It is better to be prepared than not to be.
Most of these are good to have with you while some are optional (unless under certain conditions).
Strings (絃): obviously, for when one string fails/breaks. A full set of strings (that are the same type that are strung on the qin) makes perfect sense. Preferably, they should all be prepped beforehand by tying the fly knots, thus saves you time from fiddling about with the strings trying to figure/remember how you tie them.
Pads (墊): necessary when playing on a table (which is 9 times out of 10). These are either the sandbag or the non-slip pad type. Rubber pads would not do as they have a smooth, often powdery, surface which would not keep the qin in place.
Cloth (布): a cotton handkerchief would do. This would be used to wipe the dust off the qin (you wouldn’t believe the amount of dust gathers on the surface of the qin that is then transfered onto your fingers…) and to use in stringing traditionally (unless you want you fingers to be cut off like wire to cheese). Some might say the qin bag is sufficent enough for this but having a massive wad of fabric/stiff padded nylon in your hand is not going to make stringing easier… Can be used as an aid to turning the tuning pegs that have a ridiculously smooth surface designed to make turning them near nigh impossible (you might have to wet the cloth to create more adherence).
Silk thread (絲綫): this is for if the rongko breaks and you need to make another one. The rongko shouldn’t break if it is made of silk but you don’t know about other people’s qins’ rongko (which could be made of cotton and that does break very easily). Having a spool (10m of thick pure silk thread is enough for a short thin one) at the ready means you don’t have to fiddle about with having to harvest the remaining broken, knotted and tangled threads of the ex-rongko, trying to make a new one from inferior materials in a mad frustrating rush. Also useful for replacing defective rongko made of cotton, polyester, wool, rayon and pre-twisted cord. Indeed, even better if you make one or two rongko beforehand which would save time.
Tuning peg (軫): having a spare just in case one breaks (very unlikely if made of wood, but jade pegs will smash if they hit a hard floor). Also can be used to replace defective/badly-made pegs of others.
Metal wire (鐡綫): a medium gauge metal wire, around 10″ long, that is bendable (without it snapping) is used for stringing the rongko through the holes; an almost impossible task without.
Matchstick (柴): or toothpick: good for propping up the strings on the bridge as one solution to buzzing, etc.
Piece of silk (絲): or other thin fabric. Can be used to place under the strings at the wrapping end under the qin as one solution to wolf-tones.
Rosin (松香): the kind used by cellist and violinists (any quality would do). This can be applied to the wrapping end of (non-silk) strings to cut the chances of them slipping, especially when the goose feet legs are rounded rather than square.
Of course, if you have that tuning device contraption then you should add the zither wrench to the list (and also (this is very important) learn how to use it; and yes, someone did actually need my help for this would you believe which is beggar’s belief when the whole point of having said device is to not have to ask little old me to help with stringing every time a string breaks…)