I have a couple of things that I don't see listed yet.
One is the foam noodles that are intended for kids to play with at water parks, etc. Cut them off into short sections and wrap tape around seven of them and you have a non-spill holder for paint jars.
Attach one around the circumference of a Sit-n-Spin, slice the noodle all the way around the facing edge, and you have a paint stirrer than can stir dozens of bottles at the same time,,,,,,,put a bead in each bottle, open the slice, and pop the bottle in there. Turn it very slowly while reading or something, and it will just go "shush, shush" as the beads drop, mixing all the paints you need for the next project. If you need them "right now", just put the bottles in the two positions opposite your handle, and move your hand back and forth, fairly rapidly, the beads jump up and down.
To clean threads before chap-sticking them so caps never stick again, buy a bag of the proper sized wine tasting corks from your local home brewing store, they have a cap on them that looks almost like the paint caps. When you pop one of those corks into your paint bottle, you can lay the bottle on the side as you clean the threads.
Oh, and for the quick paint stir before you use each color, put a finishing nail into a cheap plastic WalMart fingernail sander, it goes slow enough to not make the paint rise, but, fast enough to knock down any bubble from shaking. With the bead in the paint, it takes less than a minute to mix any paint you have already prepped for use.
Rex