Shellac is the answer!
I've been using it on all my woodworking for 6 or 7 years as a seal coat. Cut the Zinsser (out of the can) with an equal amount of denatured alcohol to make a #1 lb cut for sealing the pores of the wood before staining or using any other finish. It prevents blotching of the stain on most open pored woods like pine and poplar and even oak and is a great sealer for paint or any other kind of finish, even water based finishes.
There is also an amber shellac that gives a red/orange tint to wood that is interesting on some things.
I use Zinsser full strength for a finish too but, be careful about water and or alcohol stains on something like a table top.
Another trick I use to hide cracks or gaps or fill nail holes, is to mix shellac with some of the sawdust from the same wood to make a paste for wood filler. The only thing to watch for here is that if you use shellac for a final coat be careful when brushing over the patch job as the shellac will pull the patch back out.
Needless to say, it comes in spray cans too and makes for easy finishing on smaller ornate items like Christmas tree decorations.
Try it, you'll like it!
Rog