As someone who can consider to be quite penny-wise, I always appreciate great tips to make better use of your cash and, given the current Coronavirus pandemic where many might as well be stuck at home without much chance to go out buying parts and gear, or get an income, I think it's a great opportunity to share your own tips to perhaps sort some of our guitar maintaining or building needs with readily available parts and materials and, most importantly, save some cash which might be much better spent in other necessities ATM. Starting with my own, polishing frets with steel wool has the major downside of having its fine metal shavings attracted by the pickup magnets, slowly damaging them overtime. Some known techniques to minimize this are to hold a strong magnet in between the steel wool and to tape off the pickups, but these only minimize the issue. Some companies sell fret polishing erasers and cloths, which can be quite pricey. The cheap alternative? 5000 grit sandpaper. Any hardware store should have then and it costed me 50 cents a sheet, which you can then cut small squares big enough to polish the frets of your guitar. All these polishing kits are equivalent in abrasiveness to it, and I've been using it with great results. As I've been experiencing, toothpicks are your best friend when plugging screw holes. Break them in half, dab the tip in wood glue, work the glue into the hole you're plugging, snip the exceeding off with wire pliers. On a cheap guitar I've been repairing, two of the neck heel screw holes got the threads shot and couldn't be screwed tight - toothpicks certainly wouldn't do for this, so I've tried it on a larger scale. Had an old and cheap painting brush with a thin wooden handle that appeared to be maple due to its flaming; cut two plugs in its ticker area and assured they fit very snuggly. Sanded the varnish off, poured glue into the holes and gently tapped them in. Cut off the excess and drill new pilot holes. Perfect free repair (the brush remained mostly usable, as half of its handle was still intact). The best, cleanest way to dampen trem springs is by stuffing strips of foam inside of them. Cut strips of packing foam just slightly larger than the springs themselves and, using a ball pen charge as a prying tool, fold the top edge over the charge so that you can use it to push the foam into the spring. You may even keep the back plate off it won't be visible. Need to polish rust off your guitar's hardware? The abrasive blue side of those old school erasers has the perfect grit to do that without leaving marks. Parafin wax you can get at your local pharmacy (or by rubbing sheers of candle's wax onto it) is a great lubricant for open tuners, it won't damage the finish of the instrument if it drips onto it like oil does, and is recommended by some local luthiers. Mixing wood glue with fine sawdust creates a wood filler that is also as sticky as the unmixed glue, but reinforced. Perfect to glue wooden parts with slight gaps in between. All I can remember (all tested by myself) at the moment, feel free to share your own knowledge and experience!