Your homemade tweaks?

Having just read bgmyers thread on isolating cables and some of the excellent ideas our fellow audiogoners shared, I thought it would be great for us to compile a listing of all the innovative alternatives and their uses we have come up with to tweak our systems in lieu of buying them from the pricey manufacturers.

I'll start it off with having used tennis balls as isolation devices under components.
happy-sad balls from Arbor Scientific. Throw away the "happy" balls. The "Sad" balls absorb resonances amazingly well. They squash down, so nothing is needed to hold them in place. All you have to do is drop one to see how effectively it absorbs energy. They hit the floor and stay there, no bounce - apparently the energy is all dissipated as heat. I have not been able to find any source for the raw material.
Thanks for the detailed information on finding and installing the antistatic foam.
To help w/the thin cover on my Rotel CDP I first covered the entire cover (side>top>side) w/one piece of dynamat. I then cut an old Rega plinth to fit the top & after plugging the holes w/filler, put that on top then added some old lead leg weights on the plinth.

I have commercial absorption/isolation stuff underneath & the combo of everything together vs. nothing at all has helped lower the noise floor, which has resulted in letting me hear a little more detail & layering plus a slightly bigger soundstage.

I've done some stuff inside the CDP too but just the weight on top by itself at the very least keeps my somewhat large DIY PC from moving it off the Herbies grungebuster balls.
I have a Technics SL1210 turntable. Out-of-the-box the turntable has an upper midrange glare, variously attributed to the servo frequency, platter ring, motor noise coming up the spindle, etc. etc. It's none of the above, but rather the resonant ringing of the tonearm tube, which has no foam or physical damping matter inside.

I wrapped mine in Teflon pipe thread tape and it cured it. You can get a roll for about $1.00, which will wrap a lifetime of tonearms. On mine I even wrapped the knurled twist collar that attaches the headshell.

This *really* cleaned up and smoothed out the sound, and the midrange glare disappeared.

Any hollow tonearm without foam stuffing should benefit from this.