for a great all around grease Park's polylube is a foolproof route. Don't use T-9 as a rust inhibitor for seat posts / bolts, as you will be disappointed. I'm fairly sure T-9 is a wax based "oil substitute" lubricant. It's wonderful for lubing cables, freewheels and chains, but not for a tool to be used in place of grease.
Just brush on a little polylube, or spread a thin layer with your finger inside the top of the seat tube before you insert your seat post.