Found Percussion: a guide for Jeffrey Von Ragan's film and the found sound enthusiast by Greg Segal
Why "found percussion"?
The name isn't exactly precise; it's not always "found", as in by the side of the road, or in a dumpster. It can be; but there are cleaner options. They aren't free, but they can be dirt cheap. Anyone can see the appeal in that.
Beyond the term itself then, why?
With the exception of cymbals, of which no two are ever exactly alike, store-bought percussion is very close to standardized. You know when you buy it you are getting roughly the sound you've heard elsewhere, and presumably that's what you want. Under many circumstances, this is desirable. Few people want a drum with head sizes you can't find, which would have to be custom made. You could simply tune microtonally or in some eccentric way. You could put things on the heads when you hit them, or hit them in unusual ways or with unusual strikers. So standard is good. Standard means maintanence is not usually problematic.
For many drummers and percussionists, there's no reason to look any further. They don't play, or have interest in playing, music which requires anything more. In fact, anything else might get in the way.
There are those of us, though, for whom unique sounds are really important. Percussion offers almost limitless possibilities for unique sounds. Percussion is a very large field. Essentially, it's anything struck. (By this definition, the piano was originally considered a percussion instrument, before the more general "keyboard" definition came into use.)
Where is a good place to start? For me, anyplace I can get my hands on metal or wood objects as inexpensively as possible. Other materials are certainly not off limits, and I'm open to them. But they are often more fragile than metal or wood, or not loud enough. Bamboo is probably the best exception to this. Some people like glass or ceramic objects. Personally I find them too fragile, and while I would be fine to record special projects with them, using them as routinely struck objects makes me nervous.
Cheap objects are most easily found at thrift stores and garage sales. How much you want to pay is up to you. I am a cheap bastard and want to pay as little as possible. But some objects will sound so magnificent they make you gasp, and for those, sometimes you have to cough up the cash. Otherwise you'll be cringing for years to come, every time you think about passing on buying them. At least, that's what happens to me. So there's a ratio here of desirability to price.
When you first start out, there will be lots of sounds you want. Let's start with pot lids. Every pot lid is a little different, and ones with nice, bell-like tones will hook you. And this is good. Eventually though, you may find yourself at the end of what you can do with those, and pot lids will suddenly seem less desirable. My advice here is, don't give up yet. Other than those bell tones, you can find some really odd metal sounds. You'll be buying fewer pot lids, but when you find something new to you it will make you want to jump around a bit and let out some yelling sounds, scaring your fellow shoppers. If you're shy, try to abstain from that. If you're not, go for it! Enjoy your discovery.
If you are of a boy/girl scout mindset, by all means Be Prepared and bring some strikers. I usually don't bother if I'm going to a thrift store. I'll grab one or more things to strike with from the kitchen utensils section. Wood is usually easy to find, metal too. Hard plastic makes a good compromise, and can also clue you in as to what hard rubber might sound like. If you like using soft mallets, you may have to bring those. Also, be on the lookout for unique strikers! You may find some good things to use. Be open to them.
Other than pot lids, likely objects from the kitchen section include: the pots themselves, roasting pans (both sections), baking sheets, and so on. You will begin to recognize which objects are likely to offer the best possibilities. I could go into it in detail, but unfortunately I wouldn't be doing you a favor. You are better off using trial and error, because even objects which seem unlikely can surprise you. Conversely, some things you think of as tried and true might not sound good. So the best thing to do is get familiar with the basic types and your basic assumptions about them, and find a way to move quickly and effectively through whatever sized stack is in front of you. If time is not a problem, there is no need to worry about it. But for most people this is not the case. Don't get paralyzed by a fear of missing something spectacular by rushing through. Most strong, striking sounds make themselves known on the first or second hit.
Moving right along for more metal, check out the section with candle holders, housewares, chatchkes, etc. You can find some spectacular stuff in this section. So far the two best things I've found in this section have been made of pewter, a metal I'd previously dismissed as too soft. If it's thick enough, it can be strong, and will often give a gorgeous clear sound that will ring for a long, long time. This said, I would still be careful of striking too hard. I believe pewter is kind of brittle. This would account for the tightness and clarity of the sound but also the possibility of shattering. Yes, I said shattering. It may not be like a water glass, more like safety glass. But if the metal is thick enough and you use your wrists to strike, rather than your arms, you will hopefully never encounter this.
On to the wood! Usually there will be a wood section in housewares. Wooden bowls, boxes, and all sorts of things can yield good sounds. Most importantly, your chance of finding an actual instrument placed in a wrong section by mistake is probably greatest here. I have found an African slit drum (which was being displayed as a knife rack, with knives stuck in the slits), wood blocks, guiros, flutes, wind dulcimers, thunder drums....it just goes on and on. Also, interesting strikers, like ridged sticks.
Further into the tchatchkes and keepsakes and seasonal items: jingle bells; ornamental bells; decorative trumpets (as long as the tubing goes through from the mouthpiece to the bell, they're usable as long bugles.
The toy section might have electronic toys and noisemakers; toy instruments; little metallic xylophones...again, there are more possibilities than you might imagine.
Among the tools, you might find saw blades, rake tines, interesting jingly things...many possibilities.
Let's not rule out the obvious: you may actually find some musical instruments which are not hiding, but sitting out in plain sight. Even non-working instruments can be used for parts, or conversion into some other kind of insttrument.
Thrift stores are funny. You may find overpriced garbage; or you may find hidden gems for next to nothing. It's a hunt. It's a quest for cheap music makers. To me there are few things as exciting.