Best Tweaks.....

I have been tweaking my system over the years trying to improve bass and room reflection problems just like many others. Trying to keep the cost down here are some tweaks that I have found to be effective. Bass traps from GIK,
M. Green's corner tunes, and Polycrystal speaker points.
Please list your keepers...
The following are the most effective lower cost tweaks I've tried.

Herbie's Audio Lab grungebuster materials
Machina Dynamica Clever Little Clock
Marigo Audio VTS dots and bands
Xtreme A/V QuickSilver contact paste
Realtraps Mondo Trap, Mini-traps, Mini Traps HF!
Measuring tape and painters tape for positioning speakers
2 8foot ground rods pounded into the ground
Since you started with non-electrical components tweaks keepers, may not be cost effective in some......;
1. Auralex's acoustic panels & Realtrap's Minitrap are on top of my list. They have "transformed" my smallish listening room into a concert hall.
2. Roomlens Helmholtz resonator units for damping out unwanted room resonances.
3. Symposium acoustic products. I 'm using their platforms under all my equipment except for the speakers & they are brillant in bringing focus & clarity to the musical experience. I 'm using their Rollerblock Series 2 Double Stack with the top Grade 3 Superball under my CDP as well, another winner.
4. Herbie's Audio Lab products; CD Mats, IC Dampers & Hal-O damping instruments for vacuum tubes.
4. DIY Cable lifters made out of wooden disposable chopsticks.
Try putting weights on top of your components and speakers. I have two five pound weights on my sony receiver and one five pound weight on my satellite receiver and three sand ceramic tiles on each speaker. You have to move the weights around in different spots to get the sound to your liking and this takes some time to get it right but when you do... your never go back!.................
I'll also recommend Herbies tweaks. Another tweak with dramatic results is Walker's SST silver electrical contact enhancer. A freebie is to freeze your cables over night - done three times - and there will be an audible improvement in clarity, imaging and soundstaging - it is not subtle and improves after about 10 hours of use. I know it sonds crazy. And, I don;t understand how it works, but it does. A simple experiment on your onw will demonstrate it to you first hand.
ASC Tube traps. I was sceptical until I tried them and they SMOKED my Tact RCS2.0 a few years ago...showed me more than a few things about analog room correction!

I own 2 20 inch super traps and 2 11" traps....The one tweak I always keep.
Walker Audio EXTREME SST
Walker Audio Valid Points and Resonance Discs
Walker Audio Ultimate Motor Drive (motor controller)
Walker Audio Reference High Definition Links
Disc Doctor Record Miracle Cleaner - the original "yes, you need to rinse" formula

All are fundamental components for our system here...
Not necessarily the cheapest tweak...depends on who's doing it!...but I've found that a dedicated power line and some good outlets...Hubbell or Furutech ect. provided the best "tweak" for me....opened things up considerably!
Here's my two cents worth:
Quantum Symphony noise suppression/EMF stabilizer
Herbie's Grungebuster2 CD mat, Tenderfeet, Bigfooter & Halo rings for tubes
Mapleshade Silclear-on every contact you have, including tube pins
Hospital grade cryo'd outlets
1- Neuance platforms
2- Quality powercords. I'm only using Shunyata Diamondbacks and Copperheads, far from the most expensive, and still the improvement was stunning!
3- Balanced power supply for CDP and turntable. Keep them on separate filtered outlets though so the CDP doesn't pollute the TT.
4- separate dedicated homerun electrical lines with quality outlets (FIM, Furutech, many others).
Velodyne SMS-1, no question about it.

Go the the refuse can of a granite or marble company. Use the pieces of stone to mount your components on to. Good for vibration and other issues.
The best tweak by far for me is QuickSilver Gold from Xtreme Cables.........Here's some feedback.
Stop by your local granite shop (could be to the gravestone maker himself)and ask for 3cm thick remnants, which are usually no to little charge. Purchase simple rubber / soft plastic, self-stick bumpers at your local or big box hardware store (the kind of bumpers often used on kitchen cabinetry doors). Apply the bumpers to an appropriately sized granite slab and place atop and beneath your speakers, atop and beneath your equipment. Experiment with this simple idea and you may be surprised how much this helps isolate components and clean up the sound for basically no cost. And if you find the right remnants they will look killer with your gear.
Foot sanding stones (wrapped in saran wrap to keep powder from rubbing off) under the CDP. Not as good as roller balls but better than rubber or plastic feet.
Please, what is a foot sanding stone? And what do you mean by roller balls? Sounds interesting as a meaningful tweek.
Roller balls ,a steel or tungsten carbite ball that is placed between two concave metal trays.It is an isolation device that works by changing the energy of vibration into heat as the roller rolls on the horizontal axis into it's sockets.Guys is it not how the bearings work?Help out here.
Now the sanding stone is a soft stone made for removing calluses from under the feet.Dr Scholl and other brands carry them, in the drug stores.But I did not know that they can be used as a tweek,I should try them myself some time.
The foot sanding stone looks like a porous piece of ceramic. Extremely light weight but hard as stone. The porousity eliminates any resonances.
You may want to start with 3. Put them 22% in from the edges of your component which is the approximate point of minimum resonant amplitude.
stone blocks
positioning of cones