For preference I use the older GW paint pots (pictured below). At one point I used to turn them upside down as the lip around the base of the pot fits around a 2p base quite nicely. I did try corks and bits of wood, maybe ten years ago but these didn't really seem to work. Unless you are the kind of painter that pins figures to bases corks do not seem to work so well. Bits of wood did not seem to do much at all.
|About a 20mm base|
|And this one is about 50mm|