I have a set of plugs that I want to use hook hangers on and totally seal the plug. But what product should I use to fill in the hook hanger hole and encase the hanger ??

plumbers epoxy .. clear tube with red end caps ... grey playdoe type material with a black core ... mix with your fingers .. just a pinch .. stuff hole ,, have a small ram rod ready (stick)... can file/sand ... or top with minwax high performance wood filler (bondo like).. sands nice .. no signs of struggle ... both at home depot .

Thanks Tagger, I actually have some downstairs from an experiment goen wrong a couple of years ago... Wonder if its still good...

Seems like its taking me for ever to get my first set of plugs
done this year...

I've used a System3 product called Sculpwood . Although Ed's suggestion is probably cheaper.
http://www.systemthree.com/p_sculpwood_2.asp